Method for measuring scan beam light quantity distribution in scan optical system, measurement apparatus thereof, measurement evaluation apparatus thereof, and image formation apparatus using the measurement evaluation apparatus

ABSTRACT

A scan beam light quantity distribution method and apparatus using a two-dimensional area light receiving sensor  8  movable in the same direction as scan direction of a scan beam. The two-dimensional area light receiving sensor  8  detects a scan beam while moving in the scan direction of the scan beam. The scan beam received by the two-dimensional area light receiving sensor  8  is correlated with position information when stored in data storage section  10.  By using scan beam data stored in the data storage section, analysis is made on a light quantity distribution of the scan beam scanned in X-direction.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a scan beam light quantity distribution measurement method and a measurement apparatus of scan optical system, and more particularly to a scan beam light quantity distribution measurement method of a scan optical system, its measurement apparatus, and a measurement evaluation apparatus and an image formation apparatus with this measurement evaluation apparatus capable of evaluating quality of optical element for use in a scanning optical unit, for instance, influence on optical performance caused by profile irregularities, a surface defect, an internal defect and so forth while measuring light quantity distribution of the scan beam in the scanning optical unit provided at an image formation apparatus and so forth of a laser beam printer, laser facsimile and so forth.

[0003] 2. Description of the Prior Art

[0004] A write scanning optical unit used for an image formation apparatus such as a laser printer, a copy machine, a facsimile apparatus and so forth has a scan optical system constituted mainly by a laser light source, a collimator lens, various kinds of lenses and mirrors, a polygon mirror and so forth. In general, the image formation apparatus transforms laser beam generated from a laser light source into parallel light using the Collimator lens to irradiate to the polygon mirror, and parallel light is deflected by a revolution of the polygon mirror. The light beam reflected by the polygon mirror is focused as a point image on a photosensitive body by an imaging lens and a mirror system.

[0005] An electrostatic latent image is formed on the photosensitive drum by performing laser beam scan in the horizontal scan direction obtained by revolution of such a polygon mirror and in the vertical scan direction obtained by revolution of the photosensitive drum.

[0006] Further, it is known that toner is applied to the surface of the photosensitive drum having the electrostatic latent image thereon so as to change the electrostatic latent image into a sensible image, thereby forming a toner image on the surface of the photosensitive drum, subsequently, the toner image on this photosensitive drum is transferred onto a transfer sheet and fixed thereon. Thus an image is formed on this transfer sheet.

[0007] Now, when the optical elements constituting the scan optical system have abnormalities such as profile irregularities (undulation), a surface defect, an internal defect, and so forth, the scanning position of the scan beam on the photosensitive body is deviated in the horizontal scan direction, and out-of-focus in the depth direction of the scan beam occurs. Such position deviation deteriorates the peak light quantity of the scan beam and/or affects size of diameter and shape of the scan beam, thus causing faulty image formation.

[0008] Conventionally, as an apparatus for evaluating beam diameters of light beams, it is known that a pin hole or slit is made in the position corresponding to surface of the photosensitive drum and a photo-detector is set at immediately rear thereof, so that the beam diameter is measured in a stationary state, and evaluation is made to decide whether the scan optical system has a defect through judging whether a point of abrupt change is present in the value of the beam diameter thus measured.

[0009] (1) Problem Point 1

[0010] However, in this conventional measurement method of the beam diameter, when executing measurement across the entire scanning area in every predetermined pitch, for instance, when executing measurement across the entire scanning area in every 1 mm, the measurements require enormous measuring times. Further, since the measurement is executed in stationary state of the beam, there is problem that beam characteristic in scanning state cannot be measured.

[0011] Furthermore, the beam diameter is measured in the position of a fixed ratio to peak intensity of the beam and accordingly, there is the problem that evaluation based on absolute amount of the intensity is not executed.

[0012] Now, various kinds of methods have been suggested for measuring scan beam generated by optical system. As to the measurement method of the scan beam, for instance, it is described in the official gazette of the Japanese Patent Application Laid-Open No. HEI 9-43527. This official gazette discloses a scan beam measurement method and a measurement evaluation apparatus using three pieces of beam position sensors, one beam diameter sensor and one light quantity sensor equipped on a movable stage. Further, in the apparatus, the beam diameter and the light quantity of the scan beam measured using the beam diameter sensor and the light quantity sensor that move with the movable stage while ascertaining the photo-sensed position of the beam position sensor.

[0013] However, in such a conventional measurement method, there are following problems, namely:

[0014] {circle over (1)} In the conventional measurement method, measurement of the beam diameter is made using the beam diameter sensor and measurement of irregularity of light quantity is made using the light quantity sensor. However, measurement of light quantity distribution of the scan beam cannot be measured by this measurement method.

[0015] {circle over (2)} Further, in the conventional measurement method, measurement of the beam diameter can be performed at distant positions. However, this measurement method cannot execute measurement evaluation relative to neighboring beam diameters actually about degree of one pixel apart caused by restriction posed by arrangement of the beam position sensors.

[0016] {circle over (3)} Furthermore, in the conventional measurement method, measurement of the beam diameter and the light quantity is made while moving the movable stage. However, this method can measure the beam diameter at only predetermined position, and it cannot measure the beam diameter at arbitrary position in the entire horizontal scan direction. Moreover, measurement of the light quantity is executed for measurement of only the entire luminous flux of incident light, not for distribution of the light quantity of the beam.

[0017] {circle over (4)} Moreover, in the conventional measurement method, beam position is measured using the beam position sensor at three positions. However, in this measurement method, since accurate distance between respective beam position sensors is not known, it is impossible to detect distance between two points of beam, accordingly, evaluation of magnification error cannot be executed.

[0018] {circle over (5)} Still moreover, the measurement method for measuring beam position by three positions of the beam position sensors cannot execute measurement evaluation of accurate scanning line bend-amount, because there is restriction in the number of arranged beam position sensors.

[0019] {circle over (6)} Also, in the conventional measurement apparatus, scanning side beam detecting sensor is provided in the scan optical system, and three pieces of stage side beam detecting sensors are provided for detecting timing of incident scan beam at the movable stage, in which evaluation is made to execute whether position of the scanning side beam detecting sensor within the scan optical system is right while measuring time from the time that the scan beam enters into the scanning side beam detecting sensor until the time that the scan beam enters into one of the stage side beam detecting sensors. However, the conventional apparatus cannot emit beam of arbitrary light emission pattern to the stage side beam detecting sensor that moves toward the predetermined position, and also does not enable the scan beam to emit a light repeatedly because repeatability of light emission of the beam to the predetermined position is bad.

[0020] (2) Problem Point 2

[0021] Also, in this conventional measurement method of the beam diameter, when executing measurement across the entire scanning area, for instance, in every 1 mm, the measurements require enormous measuring times. Further, since the measurement is executed in stationary state of the beam, also there is malfunction that beam characteristic in scanning state cannot be measured.

[0022] As to a method for measuring the scan beam in the scan optical system, it can be considered to constitute a method by performing position measurement by the position detector of the movement means and synthesizing dot positions at this position, thereby detecting the dot position in the entire scan system.

[0023] In such a measurement apparatus, since measurement time and oscillation and so forth should be considered, instead of repeating movement/stop in every measurement, beam position measurement is usually performed while moving two-dimensional sensor serving as measuring means in the horizontal scan direction. However, when positions are stored at the time of generation of scanning reference signal and the beam positions are detected in the entire scanning area, error in the measurement time described later is generated, and since this error cannot be ignored with respect to position instrumentation error, thus it becomes problem when executing position instrumentation with high accuracy.

[0024] Hereinafter, speed fluctuation of movement mechanism and influence of observation time upon position accuracy are explained. Namely, movement speed of the movement mechanism is taken to be V (mm/sec), movement speed fluctuation is taken to be δv (mm/sec), and scanning frequency of laser 1 line is taken to be F (1/sec), in scanning time of 1 line, movement amount of the movement mechanism L (mm) is “L=(V+δv)/F”, movement amount error δL when speed fluctuation of the movable stage is about degree of ±10% is “δL=±0.1·V/F”, in the case of V=100, F=2000, δL becomes “δL=±5×10E−3 (mm)=±5 μm”.

[0025] About correspondence to this deviation from the reference position, it can be considered that a triggering PD is mounted on front stage of detection system. However, by adding the triggering PD, not only apparatus configuration becomes complicated, but also there is malfunction that configuration of control becomes complicated in that it is necessary to execute lighting control such that the scan beam enters certainly the triggering PD.

[0026] Further, in the above-described movable stage, if there is fluctuation in connection with its intervals of time from position detecting synchronizing signal until the time that position detection is executed actually, it leads to error of the beam position in the same manner. Concretely, suppose that when there is fluctuation of detection time of _PVHF under the aforementioned setting, error of 10 μm in terms of position is included. Since the beam diameter of the scan system is smaller than _(—)100 μm, there is malfunction that measurement accuracy deteriorates significantly.

[0027] Furthermore, in order to minimize fluctuation of this detection time, it is necessary to constitute systems by using hardware dedicated for detection or by using real time OS whose real time characteristic under order of μsec is guaranteed. Accordingly apparatus cost rises in comparison with the case that control is executed by use of general-purpose PC.

SUMMARY OF THE INVENTION

[0028] In view of the foregoing, it is one object of the present invention to provide a method for measuring a scan beam light quantity distribution in a scan optical system, its measurement apparatus, its measurement evaluation apparatus and an image formation apparatus using the apparatus capable of measuring dynamic light quantity distribution of the scan beam scanned in the entire scanning region of the scan optical system and performing measurement evaluation of a magnification error and a scanning line bending amount with high accuracy, thereby enabling to grasp accurate position of abnormal portion of profile irregularities (undulation), surface defects, internal defects, and so forth resulting in faulty image formation within scan optical system. Also, another object of the present invention is to execute instrumentation of the entire scan system position in the horizontal scan direction with high accuracy about a scanning optical apparatus. Further, another object of the present invention is to execute instrumentation of the entire scan system position in the horizontal scan direction with high accuracy while reducing influence of position deviation in the vertical scan direction that occurs caused by backlash of mechanism in the vertical scan direction and vibration. Furthermore, another object of the present invention is to improve convenient property of instrumentation with high accuracy due to comparison between measurement evaluation pattern and detection system position. Moreover, another object of the present invention is to improve convenience property of instrumentation with high accuracy. Still moreover, another object of the present invention is to reduce manufacturing cost.

[0029] In order to resolve such problems, in the method for measuring a scan beam light quantity distribution in a scan optical system of the present invention, the scan beam light quantity distribution measurement method of the scan optical system for measuring distribution of light quantity of a scan beam that is scanned in a predetermined direction by a scan optical system after light emission from a light source comprises the steps of: preparing a two-dimensional area light receiving element capable of moving in the same direction as a scan direction of the scan beam; detecting the scan beam by use of the light receiving element while allowing the two-dimensional area light receiving element to move in the scan direction of scan beam; storing the scan beam received by the light receiving element in data storage means while relating the scan beam received by the light receiving element to position information of the two-dimensional area light receiving element; and analyzing light quantity distribution of the scan beam scanned in the predetermined direction using data of the scan beam stored in the data storage means. In this case, it is possible to execute measurement of the dynamic light quantity distribution of the scan beam in the entire scanning region of the scan optical system.

[0030] Also, when analyzing the light quantity distribution of the scan beam, the operation is made to measure a beam diameter of a scan beam in a light quantity threshold value capable of being set arbitrarily on the basis of a light quantity in a horizontal scan direction and in a vertical scan direction at right angle to the horizontal scan direction of the scan beam, and to execute an evaluation of the scan beam diameter, wherein as the threshold value of the light quantity capable of being set arbitrarily, a threshold value is set to the same light quantity as one in which toner can be transferred normally onto a photosensitive body surface when the scan beam is irradiated on the photosensitive body surface. At this case, the operation is made to evaluate a beam diameter of a scan beam in a predetermined light quantity threshold value according to the light quantity distribution data,. The threshold value of light quantity is set on the basis of a light quantity equivalent to light quantity enabling normal toner transfer onto the surface of the photosensitive body when scan beam is applied onto the surface of the photosensitive body, thereby enabling to perform measurement of a scan beam with light quantity based on the light intensity forming an electrostatic latent image on the photosensitive body. Thus it is possible to execute evaluation agreed with the actual state to the scanning optical unit that becomes measured body.

[0031] Further, the light source is subjected to blinking control at a predetermined interval so as to modulate the scan beam emitted from the light source on pixel basis and receive the scan beam by the light receiving element at an imaging position,. When analyzing the light quantity distribution of the scan beam received by the light receiving element, a dot center-of-gravity position of respective scan beams is calculated from the analyzed light quantity distribution data to a plurality of dots measured within scanning region of the scan beam, so as to find distance-between-dot-position of distant two points. By repeatedly calculating this distance between respective adjacent dots, and to find a magnification error of the scan optical system from data in the horizontal scan direction of the scan beam obtained in such a way as to find repeatedly the distance-between-dot-position in every adjacent dots. In this case, it is possible to measure the magnification error of the scan optical system with high accuracy.

[0032] Moreover, when analyzing the light quantity distribution of scan beam received by the light receiving element, for a plurality of dots measured in a scan range of the scan beam, a dot center-of-gravity position of respective scan beams are calculated from the analyzed light quantity distribution data to find distance-between-dot-position of distant two points and by performing this calculation repeatedly for respective adjacent dots so as to obtain data of the scan beam in the vertical direction,. By using this data, it is possible to find a scanning line bendamount of the scan optical system. In this case, it is possible to measure the scanning line bend-amount of the scan optical system with high accuracy.

[0033] ## Also, the operation is made to execute about detection of the position information in the horizontal scan direction of the two-dimensional area light receiving element, to receive the scan beam through being subjected to blinking control with time interval of scanning repetition while moving the two-dimensional area light receiving element either in every predetermined pitch or moving at uniform velocity, to store information of the scan beam and the position information received by the light receiving element in the data storage section, to butt data stored in the storage section together in the horizontal scan direction of the scan beam, and to find either the magnification error or the scanning line bend-amount of the scan optical system from the data either in the horizontal scan direction or in the vertical scan direction of the scan beam. In this case, it is possible to measure the magnification error and the scanning line bend-amount of the scan optical system with high accuracy across the entire scanning region of the scan optical system.

[0034] Also, in the scan beam light quantity distribution measurement apparatus of the scan optical system of the present invention, in order to resolve the above problems, there is provided a scan beam light quantity distribution measurement apparatus of a scan optical system that comprises a light source, selection/emission control means for selecting a light emission pattern of a scan beam emitted from the light source, scanning means for scanning the scan beam emitted from the light source in a predetermined direction, detection means provided with a two-dimensional area type light receiving element for outputting an electrical signal proportional to entrapped light quantity while receiving the scan beam, movement means allowing the detection means to move either intermittently or continuously along scan direction of the scan beam scanned by the scanning means, position detection means for detecting position of the detection means, data storage means for storing data concerning light quantity of the scan beam detected by the detection means, and analysis means for analyzing light quantity distribution of the scan beam scanned in the predetermined direction using data stored in the data storage means. In this case, it is possible to execute dynamic light quantity distribution measurement of the scan beam at necessary scanning area in the entire scanning region of the scanning optical unit that becomes measured body to be measured, it is possible to measure the light quantity distribution corresponding to one pixel at arbitrary position in approximately the same condition (setting of exposure time and so forth) as the actual use in the entire scanning region, and it is possible to grasp accurate position of abnormal portion such as the profile irregularities (undulation), the surface defect, the internal defect and so forth that contribute to occurrence on faulty image formation on the basis of this light quantity distribution.

[0035] Further, the selection/emission control means have a configuration in which the light quantity of the scan beam, the time of light emission, selection as to whether the light source is made to execute lighting by only 1 point 1 time) during one scanning period, as to whether the light source is made to execute a plurality of lightings in every constant time, as to whether the light source is made to execute light emission continuously to form continuous light, or as to whether the light source is made to execute lighting with constant time intervals, lighting position and selection of the light quantity are preset to be stored therein. In this case, the selection/emission control means allow light emission to be executed in accordance with the stored light emission patterns, thereby, it is possible to execute the light quantity distribution measurement in accordance with the light emission pattern in such a way as to select the light emission pattern within one scanning period of the scan beam, accordingly, it is possible to execute variously evaluation of the scan optical system unit. For instance, as to setting of light quantity of light emission, there are a case of full light quantity and a case of halftone, it is also possible to measure to be evaluated the light quantity distribution while separating the case of the full light quantity from the case of the halftone. Further, in the case of the halftone, since the light quantity itself of the scan beam is halved, it is possible to evaluate with high sensitivity to slight abnormality of the optical element. Furthermore, when using continuous light, it is possible to detect local drop of the light quantity in the entire area of the scan optical system.

[0036] Further, the scan beam is made to modulate with pixel unit in such a way as to execute lighting of the scan beam with constant time interval, thereby it is possible to execute detection of the magnification error and the scanning line bend-amount from the data in the horizontal scan direction of the scan beam while calculating the dot center-of-gravity position of the scan beam to a plurality of dots measured within the scanning region of the scan beam.

[0037] Further, the analysis means measures the beam diameter of the scan beam in the light quantity threshold value capable of being set arbitrarily from the light quantity distribution in the horizontal scan direction and in the vertical scan direction at right angle to the horizontal scan direction of the scan beam, and executes evaluation of the scan beam diameter, since the operation is made to execute about setting of the light quantity threshold value, as the threshold value of the light quantity capable of being set arbitrarily, it can be made to set about the same light quantity as one in which toner is capable of being transferred normally onto surface of the photosensitive body as the scan beam is irradiated onto the surface of the photosensitive body, thereby it is possible to execute measurement of the scan beam with the light quantity in accordance with light intensity capable of forming electrostatic latent image on the photosensitive body, further it is possible to execute evaluation that agrees with the actual state to the scanning optical unit that becomes measured body.

[0038] Also, the selection/emission control means modulate the scan beam emitted from the light source with pixel unit in such a way as to execute blinking control of the light source with constant interval, and the analysis means calculate a dot center-of-gravity position of respective scan beams from analyzed light quantity distribution data to a plurality of dots measured within scanning region of the scan beam as the two-dimensional area light receiving element analyzes the light quantity distribution of the scan beam to find distance-between-dot-position of distant two points and can find a magnification error of the scan optical system from data in the horizontal scan direction of the scan beam obtained in such a way as to find repeatedly the distance-between-dot-position in every adjacent dots.

[0039] Also, the analysis means calculate a dot center-of-gravity position of respective scan beams from analyzed light quantity distribution data to a plurality of dots measured within scanning region of the scan beam to find distance-between-dot-position of distant two points when analyzing the light quantity distribution of the scan beam received by the two-dimensional area type light receiving element, and can find a scanning line bend-amount of the scan optical system from data in the vertical scan direction of the scan beam obtained in such a way as to find repeatedly the distance-between-dot-position in every adjacent dots.

[0040] Also, the operation is made to execute about detection of the position information in the horizontal scan direction of the two-dimensional area light receiving element, to execute light receiving of the scan beam through being subjected to blinking control with time interval of scanning repetition while allowing the two-dimensional area light receiving element either to move in every predetermined pitch or to move in uniform velocity, to execute storage of information of the scan beam and the position information received by the light receiving element in the data storage section, to execute about butting of data stored in the storage section together in the horizontal scan direction of the scan beam, and to execute finding of either the magnification error or the scanning line bend-amount of the scan optical system from the data either in the horizontal scan direction or in the vertical scan direction of the scan beam.

[0041] Also, on the occasion of high density measurement, the two-dimensional area type light receiving element is made to use on the detection optical system, therefore, detection region cannot be taken largely, as a result, it is necessary to butt detection data together, however in the meantime, since the operation can be made to execute entrapment of position information of the detection optical system accompanied with movement in high speed and high accuracy, it is possible to detect absolute position of the scan beam on the basis of the position and coordinate on the image of the two-dimensional area light receiving sensor thus obtained without increasing absolute positioning accuracy of the movement mechanism, and it is possible to measure accurately the magnification error or the scanning line bend-amount on the entire scanning area of the scan optical system.

[0042] Thus, it is possible to grasp accurate position of abnormal portion such as the profile irregularities (undulation), the surface defect, the internal defect, and so forth of the optical element within the scan optical system that contribute to occurrence on faulty image formation in such a way as to measure the magnification error or the scanning line bend-amount in the entire scanning area. Further, it is possible to clarify specification value of the profile irregularities (undulation), the surface defect, the internal defect, and so forth required for the optical element used within the scan optical system in such a way as to take correspondence to amount of deviation of the magnification error by evaluating abnormal state quantitatively, thus the specification value is capable of being reflected to design specification of the optical element.

[0043] Also, since the position detection section always detects movement position of the two-dimensional area light receiving element, even though the image data is made to obtain with the two-dimensional area light receiving element moved, measurement accuracy does not deteriorate, thus it is possible to reduce measurement time considerably.

[0044] Also, the scan beam light quantity distribution measurement apparatus has reference position detection means for detecting reference position of scanning start of said scan beam, and synchronizing signal generation means for generating synchronizing signal, wherein the selection/emission control means entraps scanning synchronizing signal generated by the synchronizing signal generation means after the scan beam is detected by the reference position detection means, and allows light emission to be executed by only one scanning period in accordance with selected light emission pattern in synchronism with this scanning synchronizing signal. In this case, it is possible to output selected light emission pattern in one scanning period on the basis of scanning synchronizing signal, and it is possible to scan scan beam of required pattern at arbitrary position of the scan optical system. For that reason, it is possible to analyze characteristic of specified portion of the scan optical system in detail.

[0045] Also, the selection/emission control means allows said scan beam to be scanned in approximately the same condition as actual use. In this case, it is possible to execute the light quantity distribution evaluation of the scan optical system unit in approximately the same condition as the actual use about the scan beam.

[0046] Also, the two-dimensional area light receiving element is capable of opening and closing light receiving surface by use a shutter so as to entrap the scan beam while selecting by only the number of required scanning line in synchronism with the scanning synchronizing signal generated by the synchronizing signal generation means after the reference position detection means detect the scan beam, further outputs stored charges to the data storage section as image signals, and has a function for removing stored charges after outputting to the data storage section. In this case, the operation can be made to execute about selection by only the number of required scanning line in synchronism with the scanning synchronizing signal generated by the synchronizing signal generation means after the reference position detection means detect the scan beam in such a way as to open and close light receiving surface by use a shutter so as to entrap the scan beam. Also, the operation is made to cause the detection data detected by the two-dimensional area light receiving element to be stored sequentially in the data storage means in high speed, thereafter to cause the input data to be eliminated, and condition is made to return to detection possible condition again, thus it is possible to plan realization of high speed measurement.

[0047] Also, the two-dimensional area type light receiving element can detect image of spot of the scan beam enlarged by an enlargement optical element. In this case, it is possible to enhance resolution of the two-dimensional area light receiving element, and it is possible to improve measurement accuracy of the light quantity distribution, the magnification error and the scanning line bend-amount.

[0048] Also, the selection/emission control means entraps the scanning synchronizing signal from the reference position detection means, and starts scanning of the scan beam in synchronism with the timing of acquisition of this signal. In this case, it is possible to execute evaluation of the beam diameter of the scan optical system in such a way as to execute signal processing of the scanning light quantity distribution data corresponding to one scanning on the basis of data obtained from the two-dimensional area light receiving element. Thus, the operation is made to measure about the beam diameter and the peak light quantity in accordance with the light quantity threshold value matched to the photosensitive body sensitivity on the basis of the scan beam light quantity distribution data in the entire scanning area, thereby it is possible to detect these abnormal values, finally, it is possible to specify abnormality of the profile irregularities (undulation), the surface defect, the internal defect, and so forth that contribute to occurrence of faulty on the image formation.

[0049] Also, the scanning means has the polygon mirror, and the selection/emission control means allows only the scan beam scanned at specific surface of the polygon mirror to be executed lighting in such a way as to count the scanning synchronization signal from the reference position detection means, thereby it is possible to increase the dot position repeatability of the scan beam scanned repeatedly as evaluation use without receiving influence of performance variation of the polygon mirror surface in such a way as to scan the scan beam by use of specific polygon mirror surface, thus it is possible to detect accurate magnification error and scanning bend-amount across the entire scanning area in such a way as to execute butting processing of the imaging data, after repeating acquisition while changing imaging position with the two-dimensional area light receiving element moved.

[0050] Also, the position detection means have the position detection triggering photo diode, and is capable of obtaining position information in the horizontal scan direction of the two-dimensional area light receiving element at incidence timing of the scan beam to the two-dimensional area light receiving element, therefore, the position detection means acquires the position information at the time point that the position detection triggering photo diode detects the scan beam, and can remove acquisition error of the position information accompanied with movement of the two-dimensional area light receiving sensor. As a result, it is possible to execute position information acquisition at the time of entrapment of the imaging data under the condition that the two-dimensional area light receiving element is moved.

[0051] Also, in order to achieve the aforementioned object, the scan beam measurement evaluation apparatus is provided with reference position detection means for detecting reference position of scanning start of scan beam output from scanning optical apparatus that executes exposure scanning of electrostatic latent image, evaluation pattern generation means for generating scan beam evaluating pattern to evaluation object pixel, light emission element control means for controlling the light emission element that irradiates light to the polygon mirror of the scanning optical apparatus on the basis of the pattern, light detection means for receiving to be detected the light quantity distribution of the scan beam by use of light receiving element, movement means for moving the light receiving element in the horizontal scan direction, position detection means for executing position detection of the light receiving element, and measurement evaluation means for executing measurement evaluation of position of the scan beam depending on scan beam position detected by the light detection means and light receiving element position detected by the position detection means in such a way as to store the position of the light receiving element detected by the position detection means in synchronism with the scan beam evaluating pattern, and to detect the scan beam by the light detection means while moving the light receiving element in the beam horizontal scan direction by use of the movement means. Accordingly, it is possible to measure a position of the entire scan system with high accuracy in such a way as to acquire the position information of movement system in synchronism with the detection evaluation pattern.

[0052] Also, in the scan beam measurement evaluation apparatus, the position detection means detect position of the vertical scan direction of said light receiving element at the same time that the position detection means detect position of the horizontal scan direction, and the measurement evaluation means execute measurement evaluation of position of the scan beam whose respective positions are stored. Accordingly, it is possible to execute instrumentation with high accuracy while reducing influence of position deviation in the vertical scan direction that is produced by vibration and/or mechanism backlash and so forth in the vertical scan direction.

[0053] Also, in the scan beam measurement evaluation apparatus, the measurement evaluation means store position of the light receiving element in synchronism with generation range of the scan beam evaluating pattern. Accordingly, it is possible to execute instrumentation of position on the entire scan system in the horizontal scan direction with high accuracy in such a way as to acquire the position information of the movement system while synchronizing with the detection evaluation pattern.

[0054] Also, in this scan beam measurement evaluation apparatus, the measurement evaluation means stores the position of the light receiving element in synchronism with. detection trigger signal generated at the trigger position at the time of actual scanning pattern generation about the scan beam evaluating pattern set independently and the detection trigger position of the position of the light receiving element. Accordingly, it is possible to execute instrumentation of the position of the entire scan system in the horizontal scan direction in high accuracy in such a way as to acquire the position information of the movement system in synchronism with the detection evaluation pattern.

[0055] Also, in this scan beam measurement evaluation apparatus, the measurement evaluation means store position of the light receiving element in synchronism with condition determined beforehand, while comparing writing pixel position that is added (accumulated) from reference position signal with position of the light receiving element obtained from the position detection means. Accordingly, it is possible to improve convenient property of high accuracy instrumentation by comparison between the measurement evaluation pattern and the detection system position.

[0056] Also, in this scan beam measurement evaluation apparatus, the measurement evaluation means store position of the light receiving element in synchronism with the first pixel clock signal after position of the scan beam is passed through position of the position detection means on the basis of beam position determined from pixel counter addition value and position information of the position detection means, as condition for storing position of the light receiving element. Accordingly, it is possible to improve convenient property of high accuracy instrumentation by comparison between the measurement evaluation pattern and the detection system position.

[0057] Also, the measurement evaluation means store position of the light receiving element in synchronism with the first pixel clock signal after the scan beam is passed through correspondence position of the position detection means while being stored the beam position determined from the pixel counter addition value corresponding to position information of the position detection means beforehand, as condition for storing position of the light receiving element. Accordingly, it is possible to improve convenient property of high accuracy instrumentation by comparison between the measurement evaluation pattern and the detection system position.

[0058] Also, in this scan beam measurement evaluation apparatus, the measurement evaluation means generate the scan beam evaluating pattern set beforehand on the basis of the position information of the light detection means input continuously, and store position information of the light receiving element and start position of the scan beam evaluating pattern in synchronism therewith, and execute measurement evaluation of the scan beam position on the entire scan system from respective position information. Accordingly, it is possible to improve convenient property of high accuracy instrumentation by comparison between the measurement evaluation pattern and the detection system position.

[0059] Also, in this scan beam measurement evaluation apparatus, the position detection means output the pulse train signal, and the evaluation pattern generation means have counter means for counting the number of pulse of the pulse train signal. Accordingly, it is possible to reduce manufacturing cost in such a way as to provide position storage function of the detection system at the evaluation pattern generation means.

[0060] Also, the electrophotographic image formation apparatus is provided with the above-described scan beam measurement apparatus, and it is possible to execute measurement evaluation of the position of the scan beam of the scanning optical apparatus for executing exposure scanning of the electrostatic latent image depending on this apparatus. Accordingly, the electrophotographic image formation apparatus is capable of giving the same action and effect as that of the above scan beam measurement evaluation apparatus.

BRIEF DESCRIPTION OF THE ATTACHED DRAWINGS

[0061]FIG. 1 is a view illustrating a scan beam light quantity distribution measurement method and measurement apparatus of scan optical system according to a first embodiment of the present invention, and outline constitution view of its measurement apparatus.

[0062]FIG. 2 is a timing chart of signal generation control section of a scan beam pattern of the first embodiment.

[0063]FIG. 3(a) shows an example of light emission pattern of laser light source, i.e., an example of 1-dot light emission pattern, image data acquired by two-dimensional area light receiving sensor and cross sectional profile of light quantity in the scan line in the first embodiment.

[0064]FIG. 3(b) shows a light emission pattern of the laser light source, i.e., light emission pattern of a dot string, image data acquired by two-dimensional area light receiving sensor and cross sectional profile of light quantity in its scanning line in the first embodiment.

[0065]FIG. 4(a) shows an example of light emission pattern of laser light source, i.e., an example of a continuous light emission pattern, image data acquired by two-dimensional area light receiving sensor and cross sectional profile of light quantity in the scan line in the first embodiment.

[0066]FIG. 4(b) shows a light emission pattern of the laser light source, i.e., light emission pattern of half tone, image data acquired by two-dimensional area light receiving sensor and cross sectional profile of light quantity in its scanning line in the first embodiment.

[0067]FIG. 5(a) shows which beam diameter of conventional scan beam in the focused position in depth direction which is evaluated on the basis of the static beam.

[0068]FIG. 5(b) shows which beam diameter of conventional scan beam in the non-focused position in depth direction which is evaluated on the basis of the static beam.

[0069]FIG. 6(a) beam diameter of the scan beam of the first embodiment in the focused position in depth direction which is evaluated on the basis of the dynamic beam.

[0070]FIG. 6(b) beam diameter of the scan beam of the first embodiment in the non-focused position in depth direction which is evaluated on the basis of the dynamic beam.

[0071]FIG. 7(a) shows beam diameter of scan beam in case a small-size side lobe is generated, which diameter is evaluated on the basis of the static beam.

[0072]FIG. 7(b) shows beam diameter of scan beam in case a large-size side lobe is generated, which diameter is evaluated on the basis of the static beam.

[0073]FIG. 8(a) shows beam diameter of scan beam in case a small-size side lobe is generated, which diameter is evaluated on the basis of the dynamic beam.

[0074]FIG. 8(b) shows beam diameter of scan beam in case a large-size side lobe is generated, which diameter is evaluated on the basis of the static beam.

[0075]FIG. 9 shows an outline configuration of a scan beam light quantity distribution measurement method and measurement apparatus for use in a scan optical system according to a second embodiment of the present invention.

[0076]FIG. 10 is a timing chart of signal generation control section of a scan beam pattern according to the second embodiment.

[0077]FIG. 11 shows image data when magnification error is evaluated at micro area of scan optical system by using dot line lighting with accurate time interval based on lighting control by laser light source modulation of the scan beam according to the second embodiment.

[0078]FIG. 12 shows image data when scan line bending amount of scan optical system is evaluated at micro area of scan optical system by using dot line lighting with accurate time interval based on lighting control by laser light source modulation of the scan beam according to the second embodiment.

[0079]FIG. 13 shows image data when measurement evaluation of magnification error and scanning line bend quantity in the entire scanning area of scan optical system are executed by use of dot line for lighting with accurate time interval by means of lighting control using laser light source modulation of the scan beam of the second embodiment.

[0080]FIG. 14 is a block diagram explaining outline configuration of a scan beam measurement evaluation apparatus as one embodiment of the invention;

[0081]FIG. 15 is a timing chart explaining operations of the scan beam measurement evaluation apparatus of FIG. 14.

[0082]FIG. 16 is a timing chart explaining operations of the scan beam measurement evaluation apparatus of FIG. 14.

[0083]FIG. 17 is an explanation view explaining action of the scan beam measurement evaluation apparatus of FIG. 14.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0084] [First Embodiment of the Invention]

[0085] Hereinafter, a first embodiment of the present invention will be described with reference to the attached drawing.

[0086] [Configuration]

[0087]FIG. 1 to FIG. 8 are views illustrating a scan beam light quantity distribution measurement method (scan beam light quantity distribution measurement/evaluation method) and a measurement apparatus (measurement/evaluation apparatus) of a scan optical system according to a first embodiment of the present invention.

[0088] Firstly, explanation refers to configuration. FIG. 1 is a view illustrating the scan beam light quantity distribution measurement apparatus. In the present embodiment, measurement of light quantity distribution is performed by setting a scan optical system 2 to this scan beam light quantity distribution measurement apparatus (scan beam measurement/evaluation apparatus) 1.

[0089] The scan optical system 2 is provided with a laser light source (light source) 3 consisting of a laser diode, a light receiving sensor 4 consisting of a photo diode as a reference position detecting means for detecting scanning start position of the scan beam, a polygon mirror (scanning means) 5 to be a revolving multiple mirror, an fθ-lens (scanning means) 6 and so forth. Further, the laser light source 3, the light receiving sensor 4, and the polygon mirror 5 are connected to the measurement apparatus 1 by connectors, so as to enable input/output to/from the measurement apparatus 1.

[0090] The scan optical system 2 is operated by the measurement apparatus 1. Further, a light beam emitted from the laser light source 3 is shaped into parallel luminous flux by Collimator lens (not depicted), and incidence of this parallel luminous flux to mirror surface of the polygon mirror 5 is performed through a cylindrical lens, before the light beam is subjected to deflection scanning by revolution of the polygon mirror 5. Further, the light beam being subjected to deflection scanning is received by the light receiving sensor 4, subsequently, being subjected to photoelectric conversion by the light receiving sensor 4 to be output to synchronizing signal generation means 7. The synchronizing signal generation means 7 generates synchronizing signal with this signal (light beam) as trigger.

[0091] On the other hand, the light beam which has been subjected to deflection scanning by the polygon mirror 5 is projected onto a straight line shaped photosensitive body image position R as a point image through long fθ lens 6. Extending direction of the straight line shaped photosensitive body image position R agrees with the horizontal scan direction of the photosensitive body (not illustrated). The point image formed, i.e., imaged, on the photosensitive body image position R is formed on a light receiving surface of a two-dimensional area light receiving sensor (two-dimensional area light receiving element) 8 consisting of CCD of the measurement apparatus 1 through an objective lens (magnification optical element) 9. The two-dimensional area light receiving sensor 8 serving as detection means (detection section) is arranged within a case 8 a, and the objective lens 9 is mounted on the case 8 a such that the objective lens 9 is installed and removed flexibly.

[0092] The light receiving sensor 8 detects a spot image of the scan beam enlarged by the objective lens 9 when received, and converts the spot image into electric signal to be output to a data storage section 10.

[0093] Further, the light receiving sensor 8 is mounted on an X-direction movable stage (moving means) 11. Below this X-direction movable stage (X-direction movable table), there is provided a Y-direction movable table (Y-direction movable stage) 12 extending in the X-direction (horizontal scan direction of the scan beam). Rails 12 a, 12 a extending in the X-direction are mounted on the Y-direction movable table 12. Further, the X-direction movable stage 11 is supported on the rails 12 a, 12 a in such a way as to be capable of moving in the longitudinal direction (X-direction). Thus, the X-direction movable stage 11 can move along the rails 12 a, 12 a.

[0094] Furthermore, a stage drive mechanism A is provided on the Y-direction movable table 12. The stage drive mechanism A includes: bearings 12 b, 12 b positioned between the rails 12 b, 12 b and mounted at the longitudinal end portion of the Y-direction table 12; a feed screw 12 c provided in parallel with the rails 12 a, 12 a and rotatably supported on the bearings 12 b, 12 b; and a pulse motor (drive motor, drive means) 12 d mounted on one end section of the Y-direction movable table 12 and having an output shaft connected to the feed screw 12 c. Moreover, the feed screw 12 c is screwed to a nut member (not depicted) provided at the movable stage 11.

[0095] The pulse motor 12 d is subjected to drive control of forward revolution or reverse revolution by a mechanism control section such as motor driver (motor drive circuit) and so forth so that the feed screw 12 c is made to revolute in forward revolution or reverse revolution so as to move the movable stage 11 in the X-direction. The mechanism control section 13 is subjected to operation control from an instrumentation section CPU 18 through a control box 14.

[0096] Further, the Y-direction movable table 12 is installed on a fixed table (not depicted) in such a way as to be capable of moving in forward and backward in Y-direction (direction at right angle to X-direction). Furthermore, the Y-direction movable table 12 is subjected to jog-mode movement control (drive control) in the Y-direction by a table drive mechanism (not depicted) having configuration identical to the stage drive mechanism A and a mechanism control section (movement control means) (not depicted) similar to the mechanism control section (movement control means) 13. This mechanism control section enables to adjust a micro-position deviation in the direction of the optical axis generated when the objective lens 9 is mounted on or removed from the case 8 a.

[0097] As described above, since the light receiving sensor (two-dimensional area sensor) 8 is equipped with the X-direction movable stage 11, the light receiving sensor 8 is moved in the X-direction by the X-direction movable stage 11 in such a way that the X-direction movable stage 11 is driven in the X-direction by the mechanism control section 13 and the stage movement mechanism A. For that reason, the two-dimensional area light receiving sensor 8 can detect the scan beam at an arbitrary position within the scanning area.

[0098] ##Further, a linear scale 15 (also optical measuring device, laser micro sensor and so forth are capable of being utilized) intervenes to be installed between the movable table 11 and the Y-direction movable table 12 as position detection means. This linear scale 15 has a main scale 15 a extending in the X-direction and being fixed along a side section that extends in the longitudinal direction of the Y-direction movable table 12, and a detection head 15 b that is mounted on the X-direction movable table 11 and the main scale 16 a and the detection head 15 b detect cooperatively movement position of the X-direction movable stage 11. Since such linear scale 15 is capable of adopting known configuration, detailed explanation is omitted. Moreover, also it is possible to use rotary encoder and so forth as the position detection means. In this case, it is possible to detect a movement position in the X-direction of the movable stage 11 in such a way as to detect revolution of the feed screw 12 c depending on the rotary encoder.

[0099] Also, it is possible to detect a movement position in the Y-direction depending on position detection means (not illustrated) that is the same means as in the X-direction.

[0100] Further, detection signal (pulse signal) from the detection head 15 b is input to a position detection section 16. The position detection section 16 finds movement amount or movement position in the X-direction of the X-direction movable stage 11 in such a way as to count the pulse signal that is the detection signal from the detection head 15 b.

[0101] Furthermore, position information of the X-direction movable stage 11 detected by the position detection section 16 is stored in a storage section (memory section or recording section) 17. It is possible to use storage medium such as memory and so forth or recording medium such as hard disk and so forth as the storage section 17.

[0102] Position data stored in the storage section 17 is output to the control box 14. Moreover, the linear scale 15 and the position detection section 16 constitute position detection means.

[0103] On the other hand, the laser light source 3 is subjected to light emission control by a lighting control section 19 that is subjected to operation control due to synchronizing signal from the synchronizing signal generation means 7. Namely, the synchronization signal generation means 7 executes operation control of the lighting control section 19 while receiving detection signal when the light receiving sensor 4 detects scanning start position of the scan beam. By this operation, the lighting control section 19 causes light emission of the laser light from the laser light source 3 to start while causing the laser light source 3 to execute light emission control.

[0104] The lighting control section (selection/emission control means) 19 drives the laser light source 3 on the basis of a plurality of light emission patterns stored in a signal storage section 20. Further, the signal storage section 20 stores therein amount of the laser light emitted by the laser light source 3, and the time that the laser light source emits. Furthermore, the lighting patterns whether the laser light source 3 is made to execute lighting of only one time during one scanning period of the laser light according to the polygon mirror 5, whether the laser light source 3 is made to execute a plurality of lightings in every constant time, whether the laser light source 3 is made to execute lighting continuously to make continuous light, or whether the laser light source 3 is made to execute lighting with constant time intervals, or so forth are stored in the signal storage section 20. Moreover, the signal storage section 20 stores therein lighting timing at the time of lighting of the laser light source 3 namely projection position onto the straight line shaped photosensitive body image position R depending on lighting of the laser light source 3, and patterns of light quantity for the sake of light emission of the laser light source 3.

[0105] Further, the lighting control section 19 is subjected to operation control depending on an order from the instrumentation section CPU 18 through the control box 14, and executes light emission control of the laser light source 3 while matching to clock signal of predetermined frequency generated from a clock signal generation means 21 in such a way as to execute emission of laser light which becomes scan beam from the laser light source 3 with the same frequency as actual use. Moreover, timing of laser light emission that becomes scan beam at this time will be described later.

[0106] Furthermore, light receiving surface of the two-dimensional area light receiving sensor 8 is in the condition of free-to-open-and-shut depending on a camera trigger shutter 22. Moreover, the two-dimensional area light receiving sensor 8 receives light of the scan beam when the shutter 22 is released. As to the camera trigger shutter 22, for instance, known electronic shutter in which liquid crystal and so forth are used, or known mechanical shutter.

[0107] Here, the control box 14 makes it possible to select mirror surface of the polygon mirror 5 that performs reflection scanning of the laser light in such a way as to count synchronization signal generated by the synchronization signal generation means 7 in compliance with the number of surfaces (6 surfaces in the present embodiment) of the polygon mirror 5. Namely, the control box 14 is capable of setting timing of light emission of the lighting control section 19 that drives the laser light source 3 in such a way that the incidence of the laser light from the laser light source 3 is executed into the specific mirror surface of the polygon mirror 5.

[0108] Further, the two-dimensional area light receiving sensor 8 stores charge when receiving scan beam. This charge storage time is determined by switching time of opening and closing of the shutter 22. The time of opening condition of the shutter 22 is set for instance, in such a way that the shutter 22 becomes closing condition when elapsing time corresponding to just one scanning of the scan beam.

[0109] In the present embodiment, when the lighting control section 19 causes the laser light source 3 to emit a light with predetermined light emission pattern, the laser light from the laser light source 3 is scanned by the polygon mirror 5 to come into scan beam, then this scan beam is imaged by the two-dimensional area light receiving sensor 8. An image signal from the two-dimensional area light receiving sensor 8 is input to the control box 14 as the image data depending on order of the instrumentation section CPU 18. The image data obtained depending on the order of the instrumentation section CPU 18 through the control box 14 is transferred to the data storage section (data storage means) 10. At this time, the position information of the imaged position obtained by the position detection section 16 is transferred from the storage section 17 to the instrumentation section CPU 18. For that reason, in the present embodiment, it is possible to grasp easily whether the two-dimensional area light receiving sensor 8 receives scan beam at which position in the scan direction of the scan beam.

[0110] Further, as described-above, the two-dimensional area light receiving sensor 8 outputs the charges that are stored on the basis of the order from the instrumentation section CPU 41 as the image signal to input to the data storage section 10. Furthermore, the instrumentation section CPU 18 transmits clear signal to the two-dimensional area light receiving sensor 8 through the control box 14 at the same time that output of the image signal to the data storage section 10 from the two-dimensional area light receiving sensor 8 is completed, followed by clearing charges stored in the two-dimensional area light receiving sensor 8 to allow the two-dimensional area light receiving sensor 8 to be returned to the condition capable of detecting the scan beam.

[0111] Moreover, the two-dimensional area light receiving sensor 8 of the present embodiment is set such that the two-dimensional area light receiving sensor 8 executes A/D conversion of the amount of the received light, for instance, executes A/D conversion of the amount of the received light into data of 10 bits to form image data of 1024 gradations.

[0112] In the present embodiment, the two-dimensional area light receiving sensor 8 executes acquisition of the image data and routine of transmission of the acquired image data toward the data storage section 10 while moving in the X-axis direction that is the horizontal scan direction, and repeats the transmission routine across the entire scanning area of the straight line shaped photosensitive body image position R to acquire the image data corresponding to one scanning line. Subsequently, signal processing section 24 executes measurement of light quantity distribution of the scan beam of the scan optical system 2 in such a way as to cause imaged light quantity distribution data to be analyzed by the control box 14.

[0113] Then, the instrumentation section CPU 18 finds the image data of the scan beam on the basis of the measurement result, and finds cross sectional profile in the scan direction and vertical scan direction depending on calculation, before representing obtained image data of the scan beam and the cross-sectional profile in the scan direction and vertical scan direction on the display section 23. In the present embodiment, the control box 14 and the instrumentation section CPU 18 constitutes analysis means, i.e., measurement evaluation means.

[0114] In the present embodiment, this measurement evaluation means, at the time that the light quantity distribution of the scan beam is made to analyze, measures beam diameter of the scan beam at a light quantity threshold value that is possible to be set arbitrary on the basis of light quantity distribution of the horizontal scan direction of the scan beam and the vertical scan direction at right angle to the horizontal scan direction to execute evaluation of diameter of the scan beam. The threshold value is set to equivalent light quantity that is one which makes it possible to transfer toner normally onto surface of the photosensitive body when the scan beam is irradiated onto the surface of the photosensitive body.

[0115] [Action]

[0116] Next, explanation refers to actions.

[0117]FIG. 2 illustrates a timing chart in a signal generation control section of a scan beam pattern of the present embodiment.

[0118] In FIG. 2, (a) indicates a fundamental signal of the laser light source 3. In this fundamental signal, in order to obtain a synchronizing signal to come to scanning start position of the scan beam, namely, in order to receive light certainly by the light receiving sensor 4, the laser light source 3 is made to emit a light while adding certain degree of allowances.

[0119] Also, in FIG. 2, (b) indicates trigger signal (light receiving trigger) on the basis of light receiving signal (light detection signal) output from this light receiving sensor 4 when the light receiving sensor receives light. In FIG. 2, (c) indicates signal that maintains timing of light receiving of the light receiving sensor 4 of (b). Further, (d) indicates a clock signal that is generated from the clock signal generation means 21 at all time.

[0120] Further, in FIG. 2, (e) indicates AND signal of (c) and (d). In FIG. 2, (f) indicates signal that is generated on the basis of a program at the instrumentation section CPU 18, and Ts is capable of being set as time which is time interval from synchronizing signal generated from the synchronizing signal generation means 7.

[0121] Furthermore, in FIG. 2, (g) indicates signal that is maintained of state of (f). In FIG. 2, (h) indicates AND signal of (e) and (g). In FIG. 2, (i) indicates the number of clock that enters into (h) counted by a counter. In FIG. 2, Tp is set as quad counter.

[0122] Moreover, in FIG. 2, (j1) to (j4) are used for light emission of the actual laser light source 3, and (j1) is 1 dot signal that is generated from AND signal of (a) and (f). In FIG. 2, (j2) is dot line signal that is generated from AND signal of (a) and (i).

[0123] Also, (j3) is continuous light that is generated from AND signal of (a) and (g). Also, (j4) is halftone that is generated from AND signal between signal (i) which has half of normal light quantity of the laser light source 3 and (a).

[0124] In the present embodiment, light emission patterns of (j1) to (j4) are stored in the signal storage section 20, and the laser light source 3 is made to emit a light in such a way as to select arbitrary the light emission pattern stored in the signal storage section 20.

[0125] Further, the light receiving sensor 4, when the laser light source 3 emits a light, receives laser light from the laser light source 3 to come to the scan beam to output light receiving signal, followed by inputting the light receiving signal to the synchronizing signal generation means 7. The synchronizing signal generation means 7, when receiving the light receiving signal, generates synchronizing signal to execute operation control of the lighting control section 19. The lighting control section 19 causes the laser light source to emit a light with any pattern of (j1) to (j4) on the basis of the synchronizing signal generated from the synchronization signal generation means 7. Further, the control box 14 controls the mechanism control section 13 depending on the order of the instrumentation section CPU 18 to execute operation control of the pulse motor 12 d to cause the feed screw 12 c to be driven rotationally, further, the control box 14 causes the movable stage 11 to move in the X-direction, and causes the two-dimensional area light receiving sensor 8 to move in the X-direction.

[0126] On this occasion, the control box 14 executes operation control of the lighting control section 19 in such a way as to open and close the shutter 22 while synchronizing with the light emission pattern of the laser light source 3. For that reason, the control box 14 allows entrapment of the scan beam to be executed by the two-dimensional area light receiving sensor 8, followed by transmitting the obtained image data to the data storage section 10.

[0127] Further, on this occasion, the control box 14 transmits the position information of the imaging position acquired by the position detection section 16 from the storage section 17 to the instrumentation section CPU 18, and causes the instrumentation section CPU 18 to grasp whether the two-dimension area light receiving sensor 8 receives the scan beam at which position in the scan direction of the scan beam.

[0128] Also, in the present embodiment, signal of the laser light source 3 is capable of emitting a light in approximately the same condition as actual use of the scanning optical unit. For instance, here, approximately the same condition as actual use is that when scan beam speed in the photosensitive body image position R is taken to be 1000 m/sec, time required for 1 scanning period is taken to be 400 μsec, length of scanning is taken to be 350 mm, and writing density is taken to be comparable to 600 dpi, cycle Tc of 1 pixel is as follows:

Tc=400×10−6/(350×600/25.4)=4.8×10−8 sec

[0129] Also, when duty ratio in 1 clock is taken to be 50% (Ta=Tb), exposure time Ta is degree of:

Ta=Tc/2=24 nsec.

[0130] Also, at this time, since speed of the scan beam is 1000 m/sec, the scan beam moves during the exposure time, and approximate movement amount S is as follows:

S=2.4×10−8×1000×103=2.4×10−2 mm=24 μm.

[0131] For that reason, in the measurement of dynamic beam, the light quantity distribution of the beam diameter spread in the scan direction, the beam diameter becomes large value of only amount corresponding to spread in the scan direction in comparison with one which is evaluated as only static beam.

[0132] In FIG. 3 and FIG. 4, (i) indicates control LD signal of the light emission patterns of the laser light source 3 according to the lighting control section 19 of the scan beam of the present embodiment. In FIG. 3 and FIG. 4, (ii) indicates indication condition that the scan beam emitted a light with the pattern of (i) is made to receive by the two-dimensional area light receiving sensor 8 in such a way as to be described above, further, the instrumentation section CPU 18 calculates light quantity distribution of the scan beam on the basis of the image signal output from the two-dimensional area light receiving sensor 8, furthermore, the instrumentation section CPU 18 sends the image data on the basis of this calculation to the display section 23, then spot shaped light quantity distribution image Lb of the scan beam on the basis of the image data is made to indicate on the display section 23. Also, (iii) of FIG. 3 and FIG. 4 indicates cross-sectional profile indication of the light quantity distribution when making the spot shaped light quantity distribution image Lb of (ii) cross section in the scan direction.

[0133] Also, when the scan beam in accordance with the scan beam light quantity measurement apparatus of the scan optical system of the present invention is projected onto the photosensitive body image position R, the scan beam is imaged on the light receiving sensor 8 through the objective lens 9. On this occasion, spot shaped scan beam is imaged on the light receiving surface of the two-dimensional area light receiving sensor 8 depending on the objective lens 9 as point image (spot image). In this case, the point image becomes in-focus on the light receiving surface of the two-dimensional area light receiving sensor 8 or becomes out-of-focus on the light receiving surface of the two dimensional area light receiving sensor 8 according to the position of the objective lens 9. The light quantity distribution of this case becomes as illustrated in FIG. 5(a), FIG. 5(b), FIG. 6(a), FIG. 6(b). FIG. 5 and FIG. 6 illustrate the light quantity distribution image Lb and its profile in cases where the point image exists on in-focus position to the focus depth direction or the point image exists on out-of-focus position to the focus depth direction. Moreover, FIG. 5 illustrates the light quantity distribution image Lb and its profile of the conventional static beam, and FIG. 6 illustrate the light quantity distribution image Lb and its profile according to the present embodiment.

[0134]FIG. 5(a) illustrates the case that the point image of the scan beam exists on in-focus position at the conventional beam diameter evaluation, FIG. 5(b) illustrates image data in out-of-focus position and cross-sectional profile at the scanning line. In this FIG. 5, peak light quantity P1 a of FIG. 5(a) differs largely from peak light quantity P1 b. Also, when obtaining beam diameter from the cross-sectional profile of the light quantity distribution image Lb, the beam diameter is obtained on the basis of ratio to peak value (peak light quantity) of intensity distribution, for instance, it is determined that the beam diameter is obtained on the basis of 1/e2≈13.5% of the peak value (peak light quantity) of the intensity distribution. According to this matter, the beam diameters obtained from the light quantity distribution image Lb and its cross-sectional profile of FIG. 5(a) and FIG. 5(b) become respective B1 a, B1 b. In the case of FIG. 5, the beam diameter B1 b of the out-of-focus position is slightly larger than the beam diameter B1 a of the in-focus position.

[0135]FIG. 6 illustrates measurement result of beam diameter depending on the measurement apparatus 1 of the present embodiment. In the present embodiment, since dynamic measurement is executed, distribution width is spread in comparison with FIG. 5. Here, on the occasion of evaluation of the beam diameter, the same light quantity threshold value is applied to the light quantity distribution image Lb and its cross-sectional profile of FIG. 5(a) and FIG. 5(b), with the result that in FIG. 5(a), beam diameter becomes B2 a, and in FIG. 5(b), beam diameter becomes B2 b, thus the beam diameter B2 a of in-focus position becomes considerably larger than the beam diameter B2 b of out-of-focus position.

[0136] For instance, it is ideal that the light quantity threshold value is determined in such a way as to match sensitivity of the photosensitive body, accordingly in the present embodiment, the light quantity threshold value is set to equivalent light quantity to one by which toner is capable of being transferred normally onto the photosensitive body when the scan beam is irradiated on the photosensitive body surface.

[0137] For that reason, evaluation of the beam diameter on the basis of dynamic measurement of the present embodiment indicates that the evaluation close to actual image formation is capable of being executed in comparison with the evaluation of the beam diameter in the static beam. Since when preliminary image formation is executed actually using the optical unit, exposure is made at the out-of-focus position, thus the preliminary image formation revealed that the light quantity for exposure is lacking, malfunction occurs on the image formation. According to this result, it is known from the fact that evaluation to the optical unit in accordance with the measurement apparatus 1 of the present embodiment is executed accurately.

[0138]FIG. 7(a) and FIG. 7(b) illustrate examples in which when measuring beam diameter according to the static beam while using the scan beam light quantity measurement apparatus of the scan optical system of the present embodiment, side lobes SL occur on the scan beam. FIG. 7(a) illustrates measurement example of the beam diameter whose size of the side lobe is small, and FIG. 7(b) illustrates measurement example of the beam diameter whose size of the side lobe is large.

[0139]FIG. 7 illustrates conventional evaluation example of the beam diameter namely, measurement example of the beam diameter. Further, FIG. 7(a) illustrates image data and cross-sectional profile at the scanning line in cases where the side lobe SL that occurs caused by optical maladjustment of the optical unit is small. FIG. 7(b) illustrates image data and cross-sectional profile at the scanning line in cases where the side lobe SL that occurs caused by optical maladjustment of the optical unit is large. Peak light quantity Q1 a in the crosssectional profile of this FIG. 7(a) is nearly the same as peak light quantity Q2 a in the cross-sectional profile of this FIG. 7(b). However, when finding the beam diameter depending on conventional method (1/e2≈13.5%), in FIG. 7(a), the beam diameter to be found becomes D1 a, while in FIG. 7(b), the beam diameter to be found becomes D1 b, as a result, value of the beam diameter D1 b of FIG. 7(b) is considerably larger than value of the beam diameter D1 a of FIG. 7(a).

[0140]FIG. 8 illustrates measurement example of the beam diameter in accordance with the measurement apparatus 1 of the present embodiment. Since dynamic measurement is executed in this FIG. 8, distribution width of light quantity of the beam diameter is spread in comparison with FIG. 7. Here, on the occasion of evaluation of beam diameter, namely measurement of the beam diameter, when applying the same light quantity threshold value as FIG. 7 to the cross-sectional profile of FIG. 8, the beam diameter in cases where the side lobe SL is small (FIG. 8(a)) becomes D2 a, while the beam diameter in cases where the side lobe SL is large (FIG. 8(b)) becomes D2 b, and value of the beam diameter D2 a is approximately the same as value of the beam diameter D2 b. Also, in this case, it is ideal that the light quantity threshold value should be made to determine while matching to sensitivity of the photosensitive body. Actually, when executing preliminary image formation using this optical unit, malfunction on the image formation does not occur. Also, in this case, it is known that evaluation to the optical unit in accordance with the present apparatus is executed accurately.

[0141] Thus, in the present embodiment, there is provided the two-dimensional area light receiving sensor 8 that is capable of moving in the same direction as the scan direction of the scan beam, and the two-dimensional area light receiving sensor 8 detects the scan beam while moving in the scan direction of the scan beam, then the operation is made to relate the scan beam received by the light receiving sensor 8 to position information to store in the data storage section 10, followed by analyzing the light quantity distribution of the scan beam that is scanned in the X-direction while using data of the scan beam stored in the data storage section 10, therefore, it is possible to execute measurement of dynamic light quantity distribution of the scan beam scanned in the entire scanning area of scan optical system 2.

[0142] Further, it is possible to measure the light quantity corresponding to 1 pixel at arbitrary position in the entire scanning area under approximately equivalent condition (setting of exposure time and so forth) to actual use (in the case of actual use), also on the basis of the light quantity distribution, it is possible to grasp accurate position of abnormal section of profile irregularities (undulation), surface defect, internal defect and so forth of the optical element within the scan optical system that become causes of generation of faulty condition on the image formation on the basis of the light quantity distribution.

[0143] Also, when analysis is made to execute about the light quantity distribution of the scan beam, measurement is made to execute about the beam diameter of the scan beam in the light quantity threshold value capable of being set arbitrary on the basis of the light quantity distribution in the horizontal scan direction and the vertical scan direction at right angle to the horizontal scan direction of the scan beam to execute evaluation of the scan beam diameter, and setting is made to execute about the light quantity threshold value capable of being set arbitrary to equivalent light quantity to light quantity on the basis of which toner is transferred normally onto the surface of the photosensitive body as the scan beam is irradiated on the surface of the photosensitive body, therefore, it is possible to execute measurement of the scan beam with the light quantity in accordance with the light intensity that forms electrostatic latent image on the photosensitive body, accordingly, it is possible to execute evaluation in conformity with actual state to the scanning optical unit that becomes object to be measured.

[0144] Further, the lighting control section 19 has a configuration in which the light quantity of the laser light (scan beam) as the laser light source 3 emits a light, the time as the laser light source 3 emits a light, selection as to whether the laser light source is made to execute lighting by only 1 point (1 time) during one scanning period of the laser light, as to whether the laser light source 3 is made to execute a plurality of lightings in every constant time, as to whether the laser light source 3 is made to execute light emission continuously to form continuous light, or as to whether the laser light source 3 is made to execute lighting with constant time intervals, lighting timing sighting position in the X-direction at straight line shaped photosensitive body image position R) at the time of lighting of the laser light source 3, and selection of the light quantity of the laser light (scan beam) are preset to be stored therein, and the lighting control section 19 allows light emission to be executed in accordance with the stored light emission patterns. For that reason, it is possible to execute the light quantity distribution measurement in accordance with the light emission pattern in such a way as to select the light emission pattern within one scanning period of the scan beam 1, accordingly, it is possible to execute variously evaluation of the scan optical system unit.

[0145] For instance, as to setting of light quantity of light emission of the laser light source 3, there are a case of full light quantity and a case of halftone, it is also possible to measure to be evaluated the light quantity distribution while separating the case of the full light quantity from the case of the halftone. Further, in the case of the halftone, since the light quantity itself of the scan beam is halved, it is possible to evaluate with high sensitivity to slight abnormality of the optical element. Furthermore, when using continuous light, it is possible to detect local drop of the light quantity in the entire area of the scan optical system.

[0146] Further, in the present embodiment, since movement position of the two-dimensional area light receiving sensor 8 is made to detect at all times depending on the position detection section 16, even though image data is made to acquire with the two-dimensional area light receiving sensor 8 moved, it is possible to reduce considerably measurement time without deterioration of measurement accuracy.

[0147] Furthermore, when the scan beam is detected by the light receiving sensor 4, the synchronization signal generation means 7 generates scanning synchronizing signal on the basis of this detected signal. Then, the lighting control section 19 entraps this scanning synchronizing signal and emits the laser light source 3 during only one scanning period in accordance with selected light emission pattern while synchronizing with this signal. As a result, it enables the laser light to emit from the laser light source while emitting the laser light source 3 on the basis of the selected light emission pattern in the one scanning period in accordance with scanning synchronizing signal, thus it is possible to scan the scan beam of required pattern at arbitrary position of the scan optical system. For that reason, it is possible to analyze in detail characteristics of specified portion of the scan optical system 2.

[0148] Moreover, since the lighting control section 19 allows the scan beam to be scanned at approximately equal condition to actual use, it is possible to execute the light quantity distribution evaluation of the scan optical system unit under approximately equal condition to actual use of the scan beam.

[0149] Further, when the light receiving sensor 8 detects the scan beam, the synchronizing signal generation means 7 generates scanning synchronizing signal on the basis of this detected signal. Then, the two-dimensional area light receiving sensor 8 is capable of selecting the scan beam to be measured since the light receiving surface is capable of being opened and closed by the shutter 22 so as to select to be entrapped the number of required scanning lines while synchronizing with this scanning synchronizing signal.

[0150] Further, since the two-dimensional area light receiving sensor 8 outputs stored charges as the image signal to the data storage section 10, and possesses function for removing stored charges after outputting to the data storage section 10, thus making it possible to detect again, accordingly, it is possible to plan implementation of high speed measurement.

[0151] Furthermore, since the two-dimensional area light receiving sensor (two-dimensional area type light receiving element) 8 is capable of enlarging to be detected the spot image of scan beam due to the objective lens 9, it is possible to enhance resolution of the two-dimensional area light receiving element 8, thus it is possible to improve measurement accuracy of the light quantity distribution.

[0152] Moreover, the lighting control section 19 entraps the scanning synchronizing signal from the synchronizing signal generation means 7 as the light receiving sensor 4 receives the scan beam, then emitting the laser light source 3 while matching the timing of acquisition of the signal, thereby, allowing the scanning to be started in connection with its scan beam synchronized with acquired timing of the scanning synchronizing signal. As a result, it is possible to execute measurement evaluation of the beam diameter of the scan optical system in such a way as to execute signal processing of the scanning light quantity distribution data corresponding to one scanning on the basis of acquired data from the two-dimensional area light receiving sensor 8.

[0153] Thus, measurement is made to execute about the beam diameter and peak light quantity in accordance with light quantity threshold value suitable for sensitivity of the photosensitive body on the basis of the scan beam light quantity distribution data in the entire scanning area, thereby, it is possible to detect these abnormal values. According to this fact, finally, it is possible to specify abnormality of the profile irregularities (undulation), the surface defect, the internal defect and so forth of the optical element within the scan optical system that contribute occurrence of faulty condition on the image formation.

[0154] Further, the light receiving sensor 4 outputs detected signal when receiving the scan beam, before inputting the detected signal to the synchronization signal generation means 7, then, the synchronization signal generation means 7 generates the scanning synchronization signal when receiving the detected signal. Subsequently, the control box 14 causes operation control of the lighting control section 19 to make it possible to execute incidence of the laser light onto the specific mirror surface of the polygon mirror 5 in connection with the laser light from the laser light source 3 in such a way as to count the scanning synchronization signal. Thus, the lighting control section 19 executes light emission control of the laser light source 3, thereby, the lighting control section 19 enables the laser light source 3 to emit a light in such a way as to make it possible to scan the laser light in connection with specific surface of the polygon mirror 5. Thus, the operation is made to execute about the scan beam so as to scan by use of specific mirror surface of the polygon mirror 5, thereby, it is possible to increase dot position repeatability of the scan beam that is scanned repeatedly for the sake of evaluation without receiving effect of performance variation of the polygon mirror surface. According to this operation, the two-dimensional area light receiving sensor 8 is made to move in the X-direction to change imaging position by this two-dimensional area light receiving sensor 8, and the two-dimensional area light receiving sensor 8 is made to receive the scan beam in every time that imaging position is changed, thus it is possible to detect the accurate light quantity distribution across the entire scanning area in such a way as to execute connection processing of the imaged image data after repeated acquisition of the image data.

[0155] Moreover, in the present embodiment, measurement method of the present invention is applied to the measurement apparatus 1 for detecting the light quantity, however the present invention is not necessarily to be limited to this configuration. For instance, in the image formation apparatus, it is possible to use it while being combined with assembly adjustment apparatus that executes assembly adjustment of parts used within the image formation apparatus while ascertaining the light quantity distribution of the beam.

[0156] [Second Embodiment]

[0157] [Configuration]

[0158]FIG. 9 to FIG. 13 are views illustrating second embodiment of a scan beam light quantity distribution measurement method and measurement apparatus of scan optical system according to the present invention, and in the present embodiment, the same number is added to the same configuration as that of the first embodiment to omit explanation.

[0159] In the present embodiment, the lighting control section 19 is made to execute lighting control of the laser light source 3 with constant intervals so as to modulate the scan beam emitted from the laser light source 3 with a pixel unit, and the two-dimensional area light receiving sensor 8 receives the scan beam at the photosensitive body image position R, then the control box 14 analyzes the light quantity distribution of the scan beam received by the two-dimensional area light receiving sensor 8. At the time that the light quantity distribution of the scan beam is made to analyze, distance between dot positions of adjacent two points is made to find in such a way as to calculate dot center of gravity position of the respective scan beams from the light quantity distribution data thus analyzed to a plurality of dots measured within the scanning area of the scan beam. Thus, magnification error and bend of the scanning line are made to find from data of the horizontal scan direction of the scan beam obtained in such a way as to find repeatedly the distance between dot positions in every adjacent two dots. This is the characteristic of the present embodiment.

[0160] For that reason, in the present embodiment, an order from the instrumentation section CPU 18 is made to transmit to the lighting control section 19 through the control box 14 to execute operation control of the lighting control section 19 so that the instrumentation section CPU 18 allows modulation signal to be output from the lighting control section 19 while matching clock of the clock signal generation means 21. Moreover, the instrumentation section CPU 18 allows the scan beam to be scanned with the same frequency as actual use in such a way as to enable laser light source LD 12 to be driven in accordance with the modulation signal output from the lighting control section 19.

[0161] Further, the instrumentation section CPU 18 allows the time interval of the dot ON/OFF (ON/OFF of the laser light source 3) of the scan beam to be stored in the signal storage section 20 of the lighting control section 19 beforehand, and allows the clock signal to be generated from the clock signal generation means 21 on the basis of data stored in the signal storage section 20, and allows the laser light source 3 to be synchronized with the clock signal through the lighting control section 19 to execute ON/OFF control in such a way as to execute operation control of the lighting control section 19 in synchronization with the clock signal. Timing of light emission of the scan beam at this time will be described later.

[0162] Furthermore, the present embodiment has a different point from the first embodiment of the present invention in that as illustrated in FIG. 9, position detection sensor (photo diode for position detection trigger) 31 is mounted on the X-direction movable stage 11 while allowing the position detection sensor 31 to be made adjacent to the two-dimensional area light receiving sensor 8. Moreover, when the two-dimensional area light receiving sensor 8 images the scan beam, the instrumentation section CPU 18 transmits the image data acquired by the two-dimensional area light receiving sensor 8 to the data storage section 10 through the control box 14. Further, the control box 14 converts the scan beam received by the position detection sensor 31 into trigger at the same time of transmission of the image data, and transmits the position information of the imaging position detected by the position detection section 16 from the storage section 17 to the instrumentation section CPU 18.

[0163] Thus, it is possible to know incidence timing of the scan beam into the two-dimensional area light receiving sensor 8 in such a way as to allow the scan beam to be detected by the position detection sensor 31. Accordingly, it is possible to know position of the two-dimensional area light receiving sensor 8 at the time of incidence of the scan beam into the two-dimensional area light receiving sensor 8 in such a way as to use detected signal of the scan beam from the position detection sensor 31 as the trigger of position information acquisition.

[0164] [Operation]

[0165] Next, operations of the scan beam light quantity distribution measurement apparatus of the scan optical system such a configuration will be described.

[0166]FIG. 10 illustrates timing chart in the lighting control section 19 of the scan beam of the present embodiment.

[0167] In FIG. 10, (a) is a fundamental signal of the laser light source 3. The fundamental signal is one in which the laser light source 3 is made to emit a light with certain degree of time intervals in order to obtain synchronizing signals that becomes scanning start position of the scan beam from the synchronizing signal generation means 7 on the basis of the detected signal from the light receiving sensor 4 in such a way as to allow the light receiving sensor 4 to receive the fundamental signal surely.

[0168] In FIG. 10, (b) is a trigger signal on the basis of the detected signal of the light receiving sensor 4, and the trigger signal causes the synchronizing signal for indicating scanning start position to be output from the synchronizing signal generation means 7.

[0169] In FIG. 10, (c) is a signal that causes Low-signal to be output from the synchronizing signal generation means 7 as the synchronizing signal to turn into scanning start position at the time point of the falling of the trigger signal of (b) to keep to Low level.

[0170] In FIG. 10, (d) is a clock signal generated by the clock signal generation means 21, and phase of the clock signal generated by the clock signal generation means 21 is adjusted to timing that signal of (c) turns into Low, the clock signal has the same frequency as that of the actual use.

[0171] In FIG. 10, (e) is drive signal for driving actually the laser light source 3 on the basis of a program of the instrumentation section CPU 18. The drive signal of this (e) is output while counting the clock signal of (d). For instance, in FIG. 10, the drive signal of (e) sets time interval Tp of the value that is subjected to 4 -pulse-count of the clock signal as quad counter.

[0172] The time interval Tp is capable of being set arbitrary, and it is possible to be taken as time interval for emitting light about the dot.

[0173] Here, the clock signal of (d) is matched accurately to the synchronizing signal of (c) generated from the synchronizing signal generation means 7 in connection with its timing, thereby, when outputting drive signal (light emission control signal) of the laser light source 3 in every time interval Tp using the clock signal, the laser light emitted from the laser light source 3 is scanned by the polygon mirror 5 to be projected onto the photosensitive body image position R, thus it is possible to improve considerably repeatability of the position in the X-direction to which the dot (point image) due to the laser light is imaged onto the straight line shaped photosensitive body image position R.

[0174] Thus, the drive signal of the laser light source 3 is capable of emitting light at the same condition as the actual use of the scanning optical unit. The same condition as the actual use is that, for instance, at the photosensitive body image position R, when scan beam speed is taken to be 1250 m/sec, time required for 1 scanning period is taken to be 400 μsec, scanning length is taken to be 340 mm, and writing density is taken to be corresponding 600 dpi, cycle Tc of 1 pixel is as follows:

Tc=272×10−6/(340×600/25.4)=3.4×10−8 sec=34 nsec.

[0175] Further, when duty ratio per 1 clock is taken to be 50% (Ta=Tb), exposure time is degree of:

Ta=Tc/2=17 nsec.

[0176] Furthermore, since the scan beam speed is 1250 m/sec at this time, interval S1 of dots of the scan beam is degree of:

S1×3.4=10−8×1250×103=4.2×10−2 mm=42 μm.

[0177] For instance, if it is set that Tp=Tc=34 nsec, it is possible to emit a light of 1/34 (nsec)=29.4 MHz. For that reason, it is possible to execute measurement evaluation of magnification error and/or bend amount of the scanning line at micro area of the scan beam as illustrated in FIG. 11, FIG. 12.

[0178] Further, for instance, if Tp=0.8 μsec is set, dot interval S2 of the scan beam becomes as follows:

S 2=0.8 μsec×1250 m/sec=1 mm

[0179] it is possible to execute measurement evaluation of linearity of 1 mm interval of scan beam and/or bend amount of the scanning line as illustrated in FIG. 13.

[0180]FIG. 11 is a view illustrating the light quantity distribution image Lb of the scan beam obtained depending on modulation control of the laser light source 3 of the present embodiment in order to evaluate magnification error at the micro area of the scan optical system.

[0181] Namely, in FIG. 11, the lighting control section 19 allows the laser light source 3 to be executed the lighting control with the accurate time interval, and allows the laser light from the laser light source 3 to be scanned by the polygon mirror 5, thereby, allowing dot line (spot light line) due to light emission of the laser light source 3 to be imaged onto the photosensitive body image position R, then the two-dimensional area light receiving sensor 8 acquires the laser light from the laser light source 3 at the photosensitive body image position R, and image data is made to find on the basis of the image signal output from the two-dimensional area light receiving sensor 8, thus, the line (dot line) of the light quantity distribution image Lb is made to display from the image data. In this FIG. 11, it is possible to execute measurement evaluation of the magnification error of the scan optical system 2 in such a way as to find intervals dx1, dx2, dx3, . . . of the line of the light quantity distribution image Lb.

[0182] Thus, the two-dimensional area light receiving sensor 8 receives dots of the laser light emitted from the laser light source 3 with the accurate time interval, then center of gravity positions of respective dots of the laser light received by the two dimensional area light receiving sensor 8 are made to calculate respectively from the image data of the light quantity distribution image Lb, subsequently, it is possible to evaluate the magnification error at micro area of the scan optical system in such a way as to measure intervals dx1, dx2, dx3, . . . of the line of the light quantity distribution image Lb.

[0183] The present embodiment is the case that a plurality of dots (spot light line of the laser light from the laser light source at the photosensitive body image position R) are entrapped within the same imaging area. The dot interval, in the case of minimum, is capable of setting to interval of writing density.

[0184] Further, with respect to detection position, measurement is made to execute on the entire scanning area in such a way as to move the X-direction movable stage 11 in the X-direction while moving the two-dimensional area light receiving sensor 8 in the scan direction (X-direction).

[0185]FIG. 12 illustrates an example of a line of the light quantity distribution image Lb obtained in the same way as FIG. 11 in order to execute measurement evaluation of the scanning line bend-amount of the scan optical system 2.

[0186] Namely, in FIG. 12, the lighting control section 19 allows the laser light source 3 to be executed lighting control with the accurate time interval, and allows the laser light of the laser light source 3 to be scanned by the polygon mirror 5, thereby the dot line (spot light line) of the laser light due to light emission of the laser light source 3 are imaged onto the photosensitive body image position R, then the two-dimensional area light receiving sensor 8 acquires the laser light from the laser light source 3 at the photosensitive body image position R, and the operation is made to find the image data on the basis of the image signal output from the two-dimensional area light receiving sensor 8, then it allows the line (dot line) of the light quantity distribution image Lb to be indicated from the image data. In this FIG. 12, the operation is made to calculate respectively about the center of gravity positions of respective dots of the laser light received by the two-dimensional area light receiving sensor 8 from the image data of the light quantity distribution image Lb, and the operation is made to measure the maximum difference dy of variation in the vertical scan direction of the line of this light quantity distribution image Lb, thus it is possible to evaluate the scanning line bend-amount on the micro area of the scan optical system 2.

[0187] In the present embodiment, the case that a plurality of dots are entrapped within the same imaging range is indicated. The dot interval is capable of being set to interval of the writing density in the minimum case.

[0188] Further, concerning the detection position, measurement is made to execute on the entire scanning area in such a way as to move the X-direction movable stage 11 in the X-direction while moving the two-dimensional area light receiving sensor 8 in the scan direction (X-direction).

[0189]FIG. 13 is a view illustrating an example in which measurement evaluation of the magnification error and the scanning line bend-amount are executed on the entire scanning area of the scan optical system 2 of the present embodiment.

[0190] Also, the example of the light quantity distribution image Lb of this FIG. 13 is obtained in such a way that, in the same way as FIG. 11, FIG. 12, the operation is made to execute lighting control of the laser light source 3 with the accurate time interval so as to scan the laser light from this laser light source 3 by the polygon mirror 5, then the two-dimensional area light receiving sensor 8 receives light (image taking) of the laser light (scan beam) thus scanned. In this case, for instance, as FIG. 13, the operation is made to image with the condition that interval of the dot is separated in such a way that one dot falls within the imaging range of the two-dimensional area light receiving sensor 8. Subsequently, the operation is made to execute about movement of the two-dimensional area light receiving sensor 8 in the X-direction by only predetermined pitch ds to image the scan beam that is emitted under the same condition as above. This is repeated about imaging positions A, B, C, D, . . . , in order to obtain the image data across the entire scanning area.

[0191] At this time, it is suitable that the operation is made to send the two-dimensional area light receiving sensor 8 sequentially by the X-direction movable stage 11 for measurement, and also it is suitable that the operation is made to send the two-dimensional area light receiving sensor 8 at uniform velocity by the X-direction movable stage 11 for continuous measurement.

[0192] The control box 14 calculates the center of gravity of the dot on the basis of data obtained by the two-dimensional area light receiving sensor 8 to obtain coordinates X0, X1, X2, X3, . . . of the horizontal scan direction of the two-dimensional area light receiving sensor 8.

[0193] Dot interval dp1 between imaging positions A and B is dpi=ds1+X1−X0.

[0194] Dot interval dp2 between imaging positions B and C is dp2=ds2+X2−X1.

[0195] Dot interval dp3 between imaging positions C and D is dp3=ds3+X3−X2.

[0196] Hereinafter, in the same way as above, it is possible to execute measurement of the magnification error in the entire scanning area while calculating respective dot intervals dp.

[0197] At this time, values of pitches ds1, ds2, ds3, . . . , of the line of the light quantity distribution image Lb are capable of being found of the position information of movement position data, movement amount data, and so forth output from the position detection section 16.

[0198] Further, similarly, the scanning line bend-amount on the entire scanning area is capable of being measured in such a way as to calculate dy that is the maximum difference of variation from the center of gravity position of the dot (light quantity distribution image Lb) of the vertical scan direction.

[0199] Thus, in the present embodiment, the lighting control section 19 is made to execute about lighting control of the laser light source 3 with constant intervals so as to modulate the scan beam emitted from the laser light source 3 with a pixel unit, and to convert the laser light into the scan beam while scanning by the polygon mirror (light scanning means) 5, then the two-dimensional area light receiving sensor 8 receives the scan beam at the photosensitive body image position R to analyze the light quantity distribution of the scan beam received by the two-dimensional area light receiving sensor 8, and at the time that the light quantity distribution of the scan beam is made to analyze, distance between dot positions of adjacent two points is made to find in such a way as to calculate dot center of gravity position of the respective scan beams from the light quantity distribution data thus analyzed to a plurality of dots measured within the scanning area of the scan beam, thus, magnification error of the scan optical system 2 is made to find from the data of the horizontal scan direction of the scan beam obtained in such a way as to find repeatedly the distance between dot positions in every adjacent two dots and the amount of bend of the scanning line of the scan optical system 2 is made to find from the data of the vertical scan direction of the scan beam, thereby, it is possible to measure the magnification error and the scanning line bend-amount of the scan optical system with high accuracy. For that reason, it is possible to grasp abnormality of the profile irregularities (undulation), the surface defect, the internal defect and so forth of the optical element within the scan optical system that contribute occurrence of faulty condition on the image formation.

[0200] Further, since the operation is made to execute about butting of the data stored in the data storage section together in the horizontal scan direction of the scan beam so as to find the magnification error or the scanning line bend-amount of the scan optical system from the data in the horizontal scan direction or in the vertical scan direction of the scan beam, it is possible to detect absolute position of the scan beam on the basis of the position of the two-dimensional area light receiving sensor 8 thus obtained and the coordinate on the image without increasing absolute positioning accuracy of the movement mechanism, thus, it is possible to measure accurately the magnification error or the scanning line bend-amount on the entire scanning area of the scan optical system.

[0201] Further, since the position detection section 16 always detects movement position of the two-dimensional area light receiving sensor 8, even though the image data is made to obtain with the two-dimensional area light receiving sensor 8 moved, measurement accuracy does not deteriorate, thus it is possible to reduce measurement time considerably.

[0202] Furthermore, selection of specific mirror surface for scanning laser light, namely, selection of specific mirror surface in a plurality of mirror surfaces of the polygon mirror 5 is capable of being executed in such a way that the operation is made to count scanning synchronizing signal from the light receiving sensor 4 and to allow the lighting control section 19 to execute lighting control of the laser light source 3 using this count value. Thus, it is possible to enhance dot position repeatability of the scan beam that is scanned repeatedly as evaluation use without receiving influence of performance variation of a plurality of mirror surfaces of the polygon mirror 5 in such a way as to scan the scan beam while using specific mirror surface of the polygon mirror 5. Moreover, it is possible to detect accurate magnification error and scanning line bend-amount across the entire scanning area in such a way that the operation is made to change about the imaging position depending on the two-dimensional area light receiving sensor 8 by moving the two-dimensional area light receiving sensor 8, and to repeat action for acquiring image of the scan beam by the two-dimensional area light receiving sensor 8, then to execute butting processing of the imaging data (image data) obtained due to the two-dimensional area light receiving sensor 8.

[0203] Moreover, since there is provided a position detection sensor 31 for detecting incidence timing of the scan beam to the two-dimensional area light receiving sensor 8, and position information from the position detection section 16 is obtained as this position detection sensor 31 detects the scan beam, it is possible to acquire the position information in the horizontal scan direction of the two-dimensional area light receiving sensor 8. For that reason, the position detection section 16 is capable of eliminating acquisition error of the position information accompanied by movement of the two-dimensional area light receiving sensor 8. As a result, it is possible to execute accurately position information acquisition at the time of entrapment of the imaging data under the condition that two-dimensional area light receiving sensor 8 is moved.

[0204] Further, with respect to the other effect, it is possible to obtain the same effect as that of the first embodiment.

[0205] [Third Embodiment]

[0206]FIG. 14 is a block diagram illustrating third embodiment of the scan beam light quantity distribution measurement apparatus according to the present invention, and for explaining outline configuration of the scan beam light quantity distribution measurement apparatus (scan beam measurement evaluation apparatus) 1 for measuring to be evaluated scan beam of the scan optical system in the electrophotographic image formation apparatus.

[0207] This scan beam light quantity distribution measurement apparatus 1 execute measurement while setting to the scan optical system 2. Moreover, in the present embodiment, light receiving sensor is made to use for detecting scanning start position of the scan beam as a reference position detection means, it is decided that a reference position signal of this sensor hereinafter is called as synchronization signal. Moreover, the same or analogous part as that of the aforementioned embodiment is explained while adding the same sign as that of the embodiment described above.

[0208] The scanning optical unit 2 has the laser light source 3 and the light receiving sensor 4. A laser diode (hereinafter referred to as LD) is used for the laser light source 3, and photo diode (hereinafter referred to as PD) for detecting scanning start position of the scan beam is used for the light receiving sensor 4. Further, the laser light source 3 and the light receiving sensor 4 are capable of being connected to the scan beam light quantity distribution measurement apparatus 1 in such a way as to be capable of inputting and outputting thereto by use of connector. Furthermore, signal input and output for the polygon mirror 5 that is rotational multiple mirror is capable of being connected by use of connector.

[0209] According to the configuration, the scan beam light quantity distribution measurement apparatus 1 irradiates the light beam from the laser light source 3 directed to reflection surface (mirror surface) of the polygon mirror 5 that is rotated, and the scan beam light quantity distribution measurement apparatus 1 allows the light beam to be reflected by the reflection surface (mirror surface) of the polygon mirror 5, thus it is possible to scan the light beam from the laser light source 3. At the time of this scanning, the scan beam (light beam) that is emitted from the laser light source 3 and scanned by the polygon mirror 5 is irradiated to the light receiving sensor 4 to be received by the light receiving sensor 4. The light receiving sensor 4, when receiving the scan beam, is capable of obtaining synchronizing signal 7 a that becomes scanning start position of the scan beam from this light receiving signal (scan beam detection signal).

[0210] Subsequently, the light beam becomes scan beam while scanning by the polygon mirror 5, then the scan beam focuses onto the photosensitive body image position R through the f θ-lens 6 to image on the straight line.

[0211] The scan beam light quantity distribution measurement apparatus 1 has the two-dimensional area light receiving sensor 8 made up of CCD as detection means. The two-dimensional area light receiving sensor 8 is capable of receiving the scan beam that is imaged onto the photosensitive body image position R due to the scanning optical unit 2. Further, spot light of the scan beam imaged onto the photosensitive body image position R due to the scanning optical unit 2 is enlarged by the objective lens 9 that is enlargement optical element to be received by two-dimensional area light receiving sensor 8. The objective lens 9 is provided at the case 8 a of the two-dimensional area light receiving sensor 8 and is installed and removed freely.

[0212] Further, subtle position deviation in the light axis direction that is produced at the time of installation and removal of the objective lens 9 to the case 8 a is adjusted by fine adjustment of the Y-direction movable table (Y-direction movable stage) 12 in the light axis direction of the objective lens 9. This point is the same as that of the first embodiment of the present invention.

[0213] The scan beam light quantity distribution measurement apparatus 1 takes a timing of light emission of the laser light (light becomes scan beam) due to the lighting control section 19 on the basis of the synchronizing signal 7 a obtained depending on the light receiving sensor 4. Further, the scan beam light quantity distribution measurement apparatus 1 allows the scan beam to be received by the two-dimensional area light source sensor 8 while opening camera trigger shutter 22 in such a way as to apply entrapment trigger of the two-dimensional area light receiving sensor 8 while matching the light emission timing of the laser light source 3.

[0214] Here, the control box 14 selects specific one of a plurality of mirror surfaces of the polygon mirror 5 in such a way as to count the synchronizing signal 7 a in accordance with the number of surface (6 faces in this example) of the polygon mirror (rotational multiple surface mirror) 5, then, the lighting control section 19 takes a timing of light emission of the laser light source 3 in such a way as to reflect to be scanned the laser light from the laser light source 3 by only the specific mirror surface thus selected.

[0215] Further, the instrumentation section CPU 18 sends an order to the control box 14, and transmits the image data obtained in such a way as to image the image data by the two-dimensional area light receiving sensor 8 to the data storage section 10 through the control box 14.

[0216] At the same time, the control box 14 transmits the position information of the imaging position that the position detection section 16 obtains on the basis of the trigger from the position detection sensor 31 and allows the storage section 17 to store from the storage section 17 to the instrumentation section CPU 18.

[0217] Further, at this time, the position detection sensor 31 applies trigger of the position information acquisition in such a way as to match incidence timing of the scan beam into the detection system by detecting the scan beam.

[0218] The two-dimensional area light receiving sensor 8 is capable of moving in the X-direction (X axis direction) that is horizontal scan direction by the X-direction movable stage 11. For that reason, the two-dimensional area light receiving sensor 8 becomes possible to detect the scan beam at arbitrary position within the scanning area. At this time, the instrumentation section CPU 18 allows the X-direction movable stage 11 to be driven by the mechanism control section 13 through the control box 14. Since the configuration for driving is the same as that of the first embodiment of the present invention, explanation thereof is omitted. Further, instrumentation of the amount of movement of the X-direction movable stage 11 is executed by the position detection section 16 using the linear scale 15 (as another measuring unit, optical measuring unit, laser micro sensor, and so forth can be utilized) that are position detection sensors. For that reason, it is possible to measure data acquisition position of the two-dimensional area light receiving sensor 8 accurately and in high speed.

[0219] The two-dimensional area light receiving sensor 8 acquires the image data while being moved by the movable stage 11 in the X axis direction that is the horizontal scan direction. Further, this acquired image data is transmitted to the data storage section 10 through the control box 14. Such routine of acquisition and transmission of the image data is repeated across within the entire scanning region by the two-dimensional area light receiving sensor 8 controlled by the control box 14, thus the image data corresponding to one scanning line. Subsequently, the signal processing section 24 executes analysis of the light quantity distribution data that is imaged, then measurement evaluation of linearity and scanning line bend-amount on the entire scanning area of the scan optical system end.

[0220] The instrumentation section CPU 18 calculates the measurement result, then it enables indication of linearity and scanning line bend-amount to be executed by the display section 23 on the entire area of the scan optical system in the scanning line.

[0221]FIG. 15 illustrates fundamental timing chart in the lighting control section 19 of the scan beam. In FIG. 15, (a) is a fundamental signal for executing drive control of the laser light source 3, in which the laser light source 3 is made to emit a light with certain degree of time intervals in order to obtain synchronizing signal 7 a that becomes scanning start position of the scan beam while allowing the scan beam depending on the polygon mirror 5 to be received by the light receiving sensor 4 surely.

[0222] In FIG. 15, signal of (b) is the synchronizing signal 7 a of FIG. 14 obtained from light receiving signal (detected signal) of the light receiving sensor 4 that becomes light receiving trigger (trigger signal) of the two-dimensional area light receiving sensor 8.

[0223] Signal of (c) is a fundamental clock signal (pixel CLOCK) 21 a of FIG. 14 that is generated at the timing of falling of (b), and is used for adjustment of deviation of clock phase produced caused by rotational irregularity and so forth of the polygon mirror 5.

[0224] Signal (d) is a counter value (pixel counter) driven by fundamental clock signal of (b), and is value (signal) that count is started after being reset to 0 at the synchronizing signal. Furthermore, the pixel counter of (d) is advanced of count value in every one cycle of fundamental clock signal of (b). Further, actual writing timing (namely its position) of the laser light source 3 is controlled by use of counter value of (d).

[0225] Signal (e) is a drive signal (Ld drive signal) that the instrumentation section CPU 18 drives actually the laser light source 3 through the lighting control section 19. Further, the instrumentation section CPU 18 enables light emission pattern of the laser light source 3 to be output in such a way as to obtain the signal of (e) from the count value of (d) on the basis of the predetermined program. For instance, in FIG. 15, the instrumentation section CPU 18 allows the laser light source 3 to emit a light depending on the lighting control 19 in such a way as to make the LD drive signal (drive signal of the laser light source 4) of (e) high in every time that the pixel counter of (d) counts four times. Thus, in FIG. 15, the time interval Tp that makes the LD drive signal high is made to set due to the quad count value of (d).

[0226] This time interval Tp is capable of being set arbitrarily. Namely, the time interval Tp is capable of being set arbitrarily in order to image the point image (dot) due to spot light of the laser light at the arbitrary position of the photosensitive body image position R in such a way as to emit the laser light source 3. Here, since the clock signal of (c) is matched accurately with the synchronizing signal 7 a in connection with its timing, the laser light source 3 emits a light due to the LD drive signal of (e), thus it is possible to improve considerably repeatability of the position of the photosensitive body image position R onto which the point image (dot) is made to image depending on the spot light of the laser light.

[0227] Next, timing on detection of movement system position will be explained.

[0228] Signal (g) that is applied correspondingly to the synchronizing signal (b) is indicated as signal (position detection trigger). Further, signal (f) is one that indicates detection position when the detection system (position detection sensor 31) moves in the X-direction. Thus, since the detection system position varies every moment as the signal (f) depending of movement of the detection system, difference between the reference position and actual evaluation pattern position becomes error of the detection system position.

[0229] Further, if delay time that the system stores actually its position from the position detection trigger signal (g) is taken to be Td, since the movement system moves during this delay time, in cases where fluctuation occurs on Td, it leads to detection error of the position information.

[0230] Moreover, in the case of writing type resolution of 600 dpi to approximately 300 mm of A4 latent width, since the number of dot in the horizontal scan direction becomes at least “7000≈300 (mm)/25.4 (mm/inch)×600 (dpi=dot/inch)”, movement of detection system at the scanning time and jitter of the clock lead to deterioration of measurement accuracy.

[0231] In order to reduce this influence, it is possible to execute timing control while providing separately position detection triggering PD (photo diode) as described-above. However, in this case, it becomes necessary to prepare the trigger PD and its measuring circuit, or it is necessary to control light emission of the beam such that the beam enters surely the trigger PD, thus the apparatus configuration becomes complicated.

[0232] In contrast with the circumstances, FIG. 16 illustrates example of position detection trigger signal depending on the scan beam light quantity distribution measurement apparatus 1 according to the present invention. Next, operations depending on the scan beam light quantity distribution measurement apparatus 1 will be explained.

[0233] A storing trigger (position detection trigger) of a signal (g1) is synchronized with rising of a pattern generation range signal of (e1), thereby, stable instrumentation of the detection system is executed without depending on position of the scan system. The pattern generation range signal generates scan beam evaluating pattern to evaluation object pixel.

[0234] Further, a storing trigger of a signal (g2) is generated at setting value (here, rising time of count value 101) of a pixel counter signal. For that reason, stable position instrumentation of the detection system is possible without depending on the position of the scan system, thus there is the effect that compensation can be executed at the time that delay time (above-described Td) occurs of generation of the position detection trigger signal until this signal is made to write in the data storage section 10 actually.

[0235] As described above, it became possible to reduce detection error in such a way as to reduce deviation between the pattern generation range signal and position detection time of the detection system. However, on the occasion that apparatus is used actually, it is necessary to guarantee that light distribution section of produced evaluation pattern is acquired by the detection system.

[0236] The laser light source 3 is subjected to light emission control using the pixel counter value, then the laser light from the laser light source 3 is scanned by the polygon mirror 5 to come into scan beam, thus the spot light of the laser light due to the scan beam is imaged as the point image onto the photosensitive body image position R. The beam position (imaging position) of the scan beam due to such pixel counter value is measured depending on detection system position output from detection system position detection means. Namely, the beam imaging position is measured by use of the position detection sensor 31 and the linear scale 15 which constitute the detection system position detection means.

[0237] This correspondence is illustrated in FIG. 17. In the graph of this FIG. 17, relationship between line GL indicating the pixel counter and variation of beam positions 1 to 8 that the detection system position detection means detect. There is part where the line GL is crossed by the beam position 1 to 8. In this case Y axis is normalized in such a way that scanning width becomes 1. The crossed section CL indicates position where the scan beam enters the position detection sensor 31 of the detection system.

[0238] Thus, it is possible to guarantee that the light distribution section of the evaluation pattern that is generated is acquired by the detection system by generating the position detection trigger signal caused by correlation between beam position that is scanned form the pixel counter value and the detection system position.

[0239] Like the standardized detection system position (predetermined detection system movement position set before hand) Ps, in the standardized beam spot position (predetermined spot imaging position set before hand) pb, the position detection trigger signal is made to generate at initial pixel rising edge that satisfies pb>ps.

[0240] As the other case, when the linearity of the movement system and scan beam is not sufficient, instrumentation of correspondence of above described pb and ps is executed before hand, and its correspondence is made to execute memory storage of LUT (look up table) and so forth, and at the time of instrumentation, the operation is made to generate about the position detection trigger signal at the first pixel rising edge that satisfies pb>LUT (ps) (LUT is correspondence table between Pb and Ps) at the time of instrumentation.

[0241] According to these means, it becomes to detect movement system detection position automatically with high accuracy without changing evaluating dot line pattern across the entire system.

[0242] Further, in cases where pattern of short range is made to execute projection evaluation for evaluation and so forth of limited spot (one or five, six of dot lines) in spite of evaluation of continuous dot line, the generation range of the pattern is made to change automatically about the position where measurement system exists at the present time, depending on the relationship between pb and ps described above, then the operation is made to execute about storage of pattern generation start position and movement system detection position of that time therewith, for that reason, it is unnecessary to execute control of the spot position from the outer section.

[0243] Further, since generation section of the position detection trigger signal 28 in synchronization with the pattern and the data storage section 10 for storing position of the position detection sensor 31 are provided, no trigger from the position detection sensor 31 in the drawing is required.

[0244] Furthermore, it becomes possible to reduce influence of the delay time Td until position of the trigger signal is stored from generation of the trigger signal in such a way as to execute directly connection between the position detection section 16 for detecting position of position detection sensor 31 and means for outputting the pattern generation range signal.

[0245] Moreover, the operation allows the pulse to be output from the position detection means that outputs the pulse in AB phase such as linear sensor, magnet-scale, encoder, and so forth, for instance, from a detection head 15 b of the linear scale 15, then the operation allows the pulse to be input to the position detection section 16. The operation is made to connect the pulse train from the detection head 15 a or the position detection section 16 to the range signal generation means that outputs pattern generation range signal directly, and allows counter function to be possessed within the range signal generation means, thereby it becomes possible to reduce cost on the entire apparatus.

[0246] According to the aforementioned configuration, since position instrumentation at the timing of actual execution of the sensor input depending on the position detection timing control becomes possible, it becomes possible to measure in relation to also micro position deviation in the vertical scan direction that is produced by vibration and/or mechanism backlash and so forth, thus, it is possible to execute measurement of the scan beam position with high accuracy. <Explanation from another view points for the aforementioned configuration>

[0247] According to the present invention, in the scan beam light quantity distribution measurement method of the scan optical system for measuring distribution of light quantity of the scan beam scanned in the predetermined direction due to scan optical system after light emission from the light source, the operation is made to prepare about the two-dimensional light receiving element capable of moving in the same direction as the scan direction of the scan beam, to detect the scan beam by the light receiving element while moving the two-dimensional area light receiving element in the scan direction of the scan beam, and to relate the scan beam that the light receiving element receives to the position information of the two-dimensional area light receiving sensor to store in the data storage means, subsequently, the operation is made to analyze the light quantity distribution of the scan beam scanned in the predetermined direction while using the data of the scan beam stored in the data storage means, thereby, it is possible to execute measurement of the dynamic light quantity distribution of the scan beam scanned in the entire scanning area of the scan optical system.

[0248] Further, the operation is made to execute about the beam diameter evaluation of the scan beam in the predetermined light quantity threshold value from among the light quantity distribution data, and to set the light quantity threshold value to equivalent light quantity to the light quantity capable of transferring toner normally onto surface of the photosensitive body as the scan beam is irradiated onto the surface of the photosensitive body, thereby it is possible to execute measurement of the scan beam with the light quantity in accordance with light intensity capable of forming electrostatic latent image on the photosensitive body, further it is possible to execute evaluation that agrees with the actual state to the scanning optical unit that becomes measured body.

[0249] Furthermore, the operation is made to execute about modulation of the scan beam emitted from the light source under the pixel unit in such a way as to execute blinking control of the light source with the constant interval, and to receive the scan beam by the light receiving element at the imaging position, then at the time that the operation is made to analyze the light quantity distribution of the scan beam that the light receiving element receives, to calculate the dot center-of-gravity position of respective scan beams from the light quantity distribution data that is analyzed to a plurality of dots measured within the scanning range of the scan beam, to find distance between dot positions of separated two points, and to find the magnification error of the scan optical system from the data of the horizontal scan direction of the scan beam obtained in such a way as to find repeatedly the distance between dot positions in every adjacent dots, thereby it is possible to measure the magnification error of the scan optical system.

[0250] Moreover, when the operation is made to execute about analysis of the light quantity distribution of the scan beam received by the light receiving element, to calculate the dot center-of-gravity position of respective scan beams from the light quantity distribution that is analyzed, to execute about acquisition of the distance between dot positions of separated two points, and to execute acquisition of the scanning line bend-amount of the scan optical system from the data in the vertical scan direction of the scan beam obtained in such a way as to find repeatedly in every adjacent dots, therefore, it is possible to measure the scanning line bend-amount of the scan optical system.

[0251] Still moreover, the operation is made to execute about detection of position information in the horizontal scan direction of the two-dimensional area light receiving element, to execute about reception of the scan beam through being subjected to blinking control at the time interval of repeated scanning by the light receiving element while moving the two-dimensional area light receiving element in every predetermined pitch or moving in uniform velocity, to execute about storage of information and position information received by the light receiving element in the data storage section, to execute about butting the data stored in the data storage section together in the horizontal scan direction of the scan beam, and to execute about acquisition of the magnification error or the scanning line bend-amount from the data in the horizontal scan direction or in the vertical scan direction of the scan beam, therefore, it is possible to measure the magnification error and the scanning line bend-amount with high accuracy across the entire scanning region of the scan optical system.

[0252] Further, the measurement apparatus is provided with the light source, selection/emission control means for selecting the light emission pattern of the scan beam emitted from the light source, scanning means for scanning the scan beam emitted from the light source in the predetermined direction, detection means consisting of the two-dimensional area type light receiving element that receives the scan beam and outputs electrical signal proportional to entrapped light quantity, movement means for moving the detection means along the scan direction of the scan beam scanned by the scanning means intermittently or continuously, position detection means for detecting position of the detection means, data storage means for storing data in relation to the light quantity of the scan beam detected by the detection means, and analysis means for analyzing the light quantity distribution of the scan beam scanned in the predetermined direction while using data stored in the data storage means, and since the measurement apparatus measures distribution of the light quantity, it is possible to execute dynamic light quantity distribution measurement of the scan beam at necessary scanning area on the entire scanning region of the scanning optical unit that becomes measured body, and it is possible to measure the light quantity distribution corresponding to one pixel in the approximately same condition (setting of exposure time and so forth) as the actual use in the entire scanning region, thus it is possible to grasp accurate position of abnormal portion of the profile irregularities (undulation), the surface defect, the internal defect and so forth of the optical element within the scan optical system that contribute to occurrence of fault on the image formation on the basis of the light quantity distribution.

[0253] Further, the selection/emission control means have a configuration in which the light quantity of the scan beam, the time of light emission, selection as to whether the light source is made to execute lighting by only 1 point (1 time) during one scanning period, as to whether the light source is made to execute a plurality of lightings in every constant time, as to whether the light source is made to execute light emission continuously to form continuous light, or as to whether the light source is made to execute lighting with constant time intervals, lighting position and selection of the light quantity are preset to be stored therein, and the selection/emission control means allow light emission to be executed in accordance with the stored light emission patterns, thereby, it is possible to execute the light quantity distribution measurement in accordance with the light emission pattern in such a way as to select the light emission pattern within one scanning period of the scan beam, accordingly, it is possible to execute variously evaluation of the scan optical system unit. For instance, as to setting of light quantity of light emission, there are a case of full light quantity and a case of halftone, it is also possible to measure to be evaluated the light quantity distribution while separating the case of the full light quantity from the case of the halftone. Further, in the case of the halftone, since the light quantity itself of the scan beam is halved, it is possible to evaluate with high sensitivity to slight abnormality of the optical element. Furthermore, when using continuous light, it is possible to detect local drop of the light quantity in the entire area of the scan optical system.

[0254] Further, the scan beam is made to modulate with pixel unit in such a way as to execute lighting of the scan beam with constant time interval, thereby it is possible to execute detection of the magnification error and the scanning line bend-amount from the data in the horizontal scan direction of the scan beam while calculating the dot center-of-gravity position of the scan beam to a plurality of dots measured within the scanning region of the scan beam.

[0255] Further, the analysis means measures the beam diameter of the scan beam in the light quantity threshold value capable of being set arbitrarily from the light quantity distribution in the horizontal scan direction and in the vertical scan direction at right angle to the horizontal scan direction of the scan beam, and executes evaluation of the scan beam diameter, since the operation is made to execute about setting of the light quantity threshold value, as the threshold value of the light quantity capable of being set arbitrarily, it can be made to set about the same light quantity as one in which toner is capable of being transferred normally onto surface of the photosensitive body as the scan beam is irradiated onto the surface of the photosensitive body, thereby it is possible to execute measurement of the scan beam with the light quantity in accordance with light intensity capable of forming electrostatic latent image on the photosensitive body, further it is possible to execute evaluation that agrees with the actual state to the scanning optical unit that becomes measured body.

[0256] Further, on the occasion of high density measurement, the two-dimensional area type light receiving element is made to use on the detection optical system, therefore, detection region cannot be taken largely, as a result, it is necessary to butt detection data together, however in the meantime, since the present invention is capable of entrapping position information of the detection optical system accompanied with movement in high speed and high accuracy, it is possible to detect absolute position of the scan beam on the basis of the position and coordinate on the image of the two-dimensional area light receiving sensor thus obtained without increasing absolute positioning accuracy of the movement mechanism, and it is possible to measure accurately the magnification error or the scanning line bend-amount on the entire scanning area of the scan optical system.

[0257] Thus, it is possible to grasp accurate position of abnormal portion of the profile irregularities (undulation), the surface defect, the internal defect and so forth of the optical element within the scan optical system that contribute to occurrence of fault on the image formation in such a way as to measure the magnification error or the scanning line bend-amount in the entire scanning area. Further, it is possible to clarify specification value of the profile irregularities (undulation), the surface defect, the internal defect, and so forth required for the optical element used within the scan optical system in such a way as to take correspondence to amount of deviation of the magnification error by evaluating abnormal state quantitatively, thus the specification value is capable of being reflected to design specification of the optical element.

[0258] Also, since the movement position of the movement means is made to always detect by the position detection means, even though the image data is acquired with the two-dimensional area light receiving element moved, it is possible to reduce considerably measurement time without decreasing measurement accuracy.

[0259] Also, there is provided reference position detection means for detecting reference position of scanning start of the scan beam and synchronizing signal generation means for generating synchronizing signal, and the selection/emission control means entrap scanning synchronizing signal generated by the synchronizing signal generation means after the scan beam is detected by the reference position detection means, and execute light emission during only one scanning period using light emission pattern selected in synchronization with this signal, thereby it is possible to output selected light emission pattern during one scanning period on the basis of the scanning synchronizing signal, thus it is possible to scan the scan beam of required pattern at arbitrary position of the scan optical system. For that reason, it is possible to analyze characteristic of specific portion of the scan optical system in detail.

[0260] Also, since the selection/emission control means allows the scan beam to be scan in approximately the same condition as the actual use, it is possible to execute the light quantity distribution evaluation of the scan optical system unit under approximately the same condition as the actual use of the scan beam.

[0261] Also, it is possible to select the scan beam to be measured by opening and closing the shutter in such a way as to select to be entrapped only required the number of the scanning lines in synchronization with the scanning synchronization signals generated by the synchronizing signal generation means.

[0262] Also, the operation is made to cause the detection data detected by the two-dimensional area light receiving element to be stored sequentially in the data storage means in high speed, thereafter to cause the input data to be eliminated, and condition is made to return to detection possible condition again, thus it is possible to plan realization of high speed measurement.

[0263] Also, the two-dimensional area light receiving element is capable of installing and removing the enlargement optical element, and enlarges to be detected spot image of the scan beam by the enlargement optical element, therefore, it is possible to increase resolution of the two-dimensional area light receiving element, thus it is possible to improve measurement accuracy of the light quantity distribution, the magnification error, and scanning line bend-amount.

[0264] Also, the selection/emission control means entraps the scanning synchronization signal from the reference position detection means, and allows the scanning of the synchronized scan beam to be started while matching the timing of acquisition of this signal, thereby it is possible to execute evaluation of the beam diameter of scan optical system in such a way as to execute signal processing of the scanning light quantity distribution data corresponding to one scanning on the basis of the data acquired from the two-dimensional light receiving element. Thus, the operation is made to measure about the beam diameter and the peak light quantity in accordance with the light quantity threshold value matched to the photosensitive body sensitivity on the basis of the scan beam light quantity distribution data in the entire scanning area, thereby it is possible to detect these abnormal values, finally, it is possible to specify abnormality of the profile irregularities (undulation), the surface defect, the internal defect, and so forth that contribute to occurrence of faulty on the image formation.

[0265] Also, the scanning means has the polygon mirror, and the selection/emission control means allows only the scan beam scanned at specific surface of the polygon mirror to be executed lighting in such a way as to count the scanning synchronization signal from the reference position detection means, thereby it is possible to increase the dot position repeatability of the scan beam scanned repeatedly as evaluation use without receiving influence of performance variation of the polygon mirror surface in such a way as to scan the scan beam by use of specific polygon mirror surface, thus it is possible to detect accurate magnification error and scanning bend-amount across the entire scanning area in such a way as to execute butting processing of the imaging data, after repeating acquisition while changing imaging position with the two-dimensional area light receiving element moved.

[0266] Further, the position detection means have the position detection triggering photo diode, and is capable of obtaining position information in the horizontal scan direction of the two-dimensional area light receiving element at incidence timing of the scan beam to the two-dimensional area light receiving element, therefore, the position detection means acquires the position information at the time point that the position detection triggering photo diode detects the scan beam, and can remove acquisition error of the position information accompanied with movement of the two-dimensional area light receiving sensor. As a result, it is possible to execute position information acquisition at the time of entrapment of the imaging data under the condition that the two-dimensional area light receiving element is moved.

[0267] Also, the scan beam measurement evaluation apparatus is provided with reference position detection means for detecting reference position of scanning start of scan beam output from scanning optical apparatus that executes exposure scanning of electrostatic latent image, evaluation pattern generation means for generating scan beam evaluating pattern to evaluation object pixel, light emission element control means for controlling the light emission element that irradiates light to the polygon mirror of the scanning optical apparatus on the basis of the pattern, light detection means for receiving to be detected the light quantity distribution of the scan beam by use of light receiving element, movement means for moving the light receiving element in the horizontal scan direction, position detection means for executing position detection of the light receiving element, and measurement evaluation means for executing measurement evaluation of position of the scan beam depending on scan beam position detected by the light detection means and light receiving element position detected by the position detection means in such a way as to store the position of the light receiving element detected by the position detection means in synchronism with the scan beam evaluating pattern, and to detect the scan beam by the light detection means while moving the light receiving element in the beam horizontal scan direction by use of the movement means. Accordingly, it is possible to measure a position of the entire scan system with high accuracy in such a way as to acquire the position information of movement system in synchronism with the detection evaluation pattern.

[0268] Also, in this scan beam measurement evaluation apparatus, the position detection means detects the position of the vertical scan direction at the same time that the light receiving element detects the position of the horizontal scan direction, further the measurement evaluation means store these respective positions to execute measurement evaluation of the scan beam. Accordingly, it is possible to execute instrumentation with high accuracy in such a way as to reduce influence of position deviation in the vertical direction that occurs caused by backlash of the mechanism in the vertical direction or vibration.

[0269] Also, in this scan beam measurement evaluation apparatus, the measurement evaluation means stores a position of the light receiving element in synchronism with generation range of the scan beam evaluating pattern. Accordingly, it is possible to execute instrumentation of the position of the entire scan system in the horizontal scan direction in high accuracy in such a way as to acquire the position information of the movement system in synchronism with the detection evaluation pattern.

[0270] Also, in this scan beam measurement evaluation apparatus, the measurement evaluation means stores the position of the light receiving element in synchronism with detection trigger signal generated at the trigger position at the time of actual scanning pattern generation about the scan beam evaluating pattern set independently and the detection trigger position of the position of the light receiving element. Accordingly, it is possible to execute instrumentation of the position of the entire scan system in the horizontal scan direction in high accuracy in such a way as to acquire the position information of the movement system in synchronism with the detection evaluation pattern.

[0271] Also, in this scan beam measurement evaluation apparatus, the measurement evaluation means compares the writing pixel position added up from the reference position signal with the position of the light receiving element obtained from the position detection means, and stores the position of the light receiving element in synchronism with the condition determined beforehand. Accordingly, it is possible to improve convenient property of high accuracy instrument by comparison between the measurement evaluation pattern and the detection system position.

[0272] Also, in this scan beam measurement evaluation apparatus, the measurement evaluation means stores the position of the light receiving element in such a way that the position of the position detection means is made to synchronize with the first pixel clock signal after the position of the scan beam is passed through from both the beam position determined from the pixel counter addition value and the position information of the position detection means as the condition for storing the position of the light receiving element. Accordingly, it is possible to improve convenient property of high accuracy instrumentation depending on comparison between the measurement evaluation pattern and the detection system position.

[0273] Also, the measurement evaluation means stores the beam position determined from the pixel counter addition value corresponding to the position information of the position detection means beforehand as the condition for storing the position of the light receiving element, after the scan beam is passed through the correspondence position of the position detection means, the light receiving element position is made to store in synchronism with the first pixel clock signal. Accordingly, it is possible to improve the convenience property of high accuracy instrumentation.

[0274] Also, in this scan beam measurement evaluation apparatus, the measurement evaluation means produces the scan beam evaluating pattern set beforehand on the basis of the position information of the light detection means input continuously, and stores the position information of the light receiving element and start position of the scan beam evaluating pattern in synchronism therewith, then the measurement evaluation means executes measurement evaluation of the scan beam position on the entire scan system from respective position information. Accordingly, it is possible to improve convenience property of high accuracy instrumentation due to comparison between the measurement evaluation pattern and the detection system position.

[0275] Also, in this scan beam measurement evaluation apparatus, the position detection means output the pulse train signal, and the evaluation pattern generation means have counter means for counting the number of pulse of the pulse train signal. Accordingly, it is possible to reduce manufacturing cost in such a way as to provide position storage function of the detection system at the evaluation pattern generation means.

[0276] Also, the electrophotographic image formation apparatus is provided with the above-described scan beam measurement apparatus, and it is possible to execute measurement evaluation of the position of the scan beam of the scanning optical apparatus for executing exposure scanning of the electrostatic latent image depending on this apparatus. Accordingly, the electrophotographic image formation apparatus is capable of giving the same action and effect as that of the above scan beam measurement evaluation apparatus. 

What is claimed is:
 1. A method for measuring scan beam light quantity distribution in a scan optical system, i.e., distribution of light quantity of a scan beam emitted from a light source to be used for scanning in a predetermined direction, the method comprising steps of: preparing a two-dimensional area light receiving element capable of moving in a direction identical to a scan direction of said scan beam; detecting said scan beam by use of said light receiving element while moving said two-dimensional area light receiving element in said scan direction of scan beam; storing the scan beam received by the light receiving element in data storage means while relating the received scan beam to position information of said two-dimensional area light receiving element; and analyzing light quantity distribution of said scan beam scanning in said predetermined direction while using data of the scan beam stored in said data storage means.
 2. The method as claimed in claim 1, said analyzing step including steps of: measuring a beam diameter of a scan beam in a light quantity threshold value capable of being set arbitrarily on the basis of the light quantity in a horizontal scan direction of said scan beam and in a vertical scan direction at right angle to said horizontal scan direction; and evaluating said scan beam diameter, wherein said threshold value of the light quantity capable of being set arbitrarily is set to light quantity equivalent to light quantity which enables normal transfer of toner onto a photosensitive body surface when said scan beam is irradiated on the photosensitive body surface.
 3. The method as claimed in claim 1, further comprising steps of; pixel-basis-modulating the scan beam emitted from said light source by controlling the light source so as to blink at a constant interval; receiving said scan beam by said light receiving element at an imaging position; and analyzing the light quantity distribution of the scan beam received by the light receiving element through steps of: calculating a dot center-of-gravity position of respective scan beams from analyzed light quantity distribution data against a plurality of dots measured within scanning region of said scan beam to find distance-between-dot-position of distant two points; and finding a magnification error of said scan optical system from data in the horizontal scan direction of said scan beam obtained in such a way as to find repeatedly the distance-between-dot-position in every adjacent dots.
 4. The method as claimed in claim 3, wherein the analyzing step for analyzing the light quantity distribution of the scan beam received by the light receiving element is performed through steps of: calculating a dot center-of-gravity position of respective scan beams from analyzed light quantity distribution data against a plurality of dots measured within scanning region of said scan beam to find distance-between-dot-position of distant two points; and finding a scanning line bend-amount of said scan optical system from data in the vertical scan direction of said scan beam obtained in such a way as to find repeatedly the distance-between-dot-position in every adjacent dots.
 5. The method as claimed in claim 2, further comprising steps of: detecting the position information in the horizontal scan direction of said two-dimensional area light receiving element; receiving the scan beam by the light reception element while the scan beam is controlled to blink at a repeated scan time interval by moving the two-dimensional area light receiving element either with a predetermined pitch or; storing information of the scan beam received by the light receiving element and said position information in said data storage section; arranging (chaining) data stored in the storage section in the horizontal scan direction of the scan beam; and calculating either a magnification error or a scanning line bend-amount of said scan optical system using the data of the horizontal scan direction or the vertical scan direction of the scan beam.
 6. A scan beam light quantity distribution measurement apparatus of a scan optical system, said apparatus comprising: a light source; selection/emission control means for selecting a light emission pattern of a scan beam emitted from the light source; scanning means for scanning the scan beam emitted from said light source in a predetermined direction; detection means having a two-dimensional area type light receiving element for outputting an electrical signal proportional to entrapped light quantity while receiving said scan beam; movement means allowing said detection means to move either intermittently or continuously along scan direction of the scan beam scanned by the scanning means; position detection means for detecting position of said detection means; data storage means for storing data concerning light quantity of the scan beam detected by said detection means; and analysis means for analyzing light quantity distribution of the scan beam used for scanning in said predetermined direction using data stored in said data storage means.
 7. The scan beam light quantity distribution measurement apparatus as claimed in claim 6, wherein said selection/emission control means is configured so as to set and store following parameters: the light quantity of the scan beam emitted from said light source; time of light emission; selection of modes of said light source, i.e., only one point is lighted during one scanning period, or a plurality of points are lighted in every constant time interval, or continuously lighted, or lighted in every constant time interval; and selection of lighting position and the light quantity at the time of the lighting; so that light is emitted in accordance with light emission pattern thus stored.
 8. The scan beam light quantity distribution measurement apparatus as claimed in claim 6, wherein said analysis means measures a beam diameter of the scan beam in a light quantity threshold value that can be set arbitrarily in horizontal scan direction of said scan beam and in vertical scan direction at right angle to the horizontal scan direction, and evaluates said scan beam diameter, thereby enabling to set the light quantity threshold value that can be arbitrarily set to light quantity equivalent to light quantity enabling normal toner transfer onto the photosensitive body surface when said scan beam is irradiated on the photosensitive body surface.
 9. The scan beam light quantity distribution measurement apparatus as clamed in claim 6, wherein said selection/emission control means is configured so as to control the light source to blink at a predetermined interval so as to modulate, the scan beam emitted from said light source on pixel basis; and said analysis means analyzes the light quantity distribution of the scan beam received by the two-dimensional area type receiving element by calculating a dot center-of-gravity position of respective scan beams according to the analyzed light quantity distribution data against a plurality of dots measured within scanning region of said scan beam so as to calculate distance between distant two point positions, which calculation is repeated for every adjacent dots, thereby finding a magnification error of said scan optical system from data of the horizontal scan direction of said scan beam.
 10. The scan beam light quantity distribution measurement apparatus as claimed in claim 6, wherein the analysis of the light quantity distribution of the scan beam received by the two-dimensional area type receiving element by calculating a dot center-of-gravity position of respective scan beams according to the analyzed light quantity distribution data against a plurality of dots measured within scanning region of said scan beam so as to calculate distance between distant two point positions, which calculation is repeated for every adjacent dots, thereby finding a scan line bend-amount of said scan optical system from data in the vertical scan direction of said scan beam.
 11. The scan beam light quantity distribution measurement apparatus as claimed in claim 6, wherein analysis is performed by detecting the position information in the horizontal scan direction of said two-dimensional area light receiving element; receiving the scan beam by the light reception element while the scan beam is controlled to blink at a repeated scan time interval by moving the two-dimensional area light receiving element either with a predetermined pitch or uniform velocity; storing information of the scan beam received by the light receiving element and said position information in said data storage section; arranging (chaining) data stored in the storage section in the horizontal scan direction of the scan beam; and calculating either a magnification error or a scanning line bend-amount of said scan optical system using the data of the horizontal scan direction or the vertical scan direction of the scan beam.
 12. The scan beam light quantity distribution measurement apparatus as claimed in claim 6, further comprising: reference position detection means for detecting a scan start reference position of said scan beam; and synchronizing signal generation means for generating a synchronizing signal, wherein said selection/emission control means fetches a scan synchronizing signal generated by said synchronizing signal generation means after the scan beam is detected by said reference position detection means, and causes light emission by only one scanning period in accordance with selected light emission pattern in synchronism with this scanning synchronizing signal.
 13. The scan beam light quantity distribution measurement apparatus as claimed in claim 6, wherein said selection/emission control means causes said scan beam to perform scanning in a condition approximately identical to actual use.
 14. The scan beam light quantity distribution measurement apparatus as claimed in claim 12, wherein said two-dimensional area light receiving element has a light receiving surface that can be opened and closed by use of a shutter so as to selectively fetch a desired number of scan lines in synchronism with the scan synchronizing signal generated by said synchronizing signal generation means after the scan beam is detected by said reference position detection means, and has a function to output accumulated charges as image signals to said data storage section and to remove charge accumulated after output to said data storage section.
 15. The scan beam light quantity distribution measurement apparatus as claimed in claim 6, wherein said two-dimensional area type light receiving element detects image of spot of the scan beam enlarged by an enlargement optical element.
 16. The scan beam light quantity distribution measurement apparatus as claimed in claim 12, wherein said selection/emission control means fetches the scan synchronizing signal from said reference position detection means, and starts scanning by the scan beam in synchronism with the timing of this signal fetch.
 17. The scan beam light quantity distribution measurement apparatus as claimed in claim 6, wherein said scanning means has a polygon mirror, and said selection/emission control means counts the scan synchronization signal from the reference position detection means so as to light only a scan beam scanned on a particular surface of the polygon mirror.
 18. The scan beam light quantity distribution measurement apparatus as claimed in claim 7, wherein said position detection means has a position detection triggering photo-diode, and can acquire position information in the horizontal scan direction of said two-dimensional area light receiving element at incidence timing of the scan beam into said two-dimensional area light receiving element.
 19. A scan beam measurement evaluation apparatus comprising: reference position detection means for detecting a scan start reference position of a scan beam output from a scanning optical apparatus for executing exposure scanning of an electrostatic latent image; evaluation pattern generation means for generating a scan beam evaluating pattern to a pixel to be evaluated; light emission element control means for controlling a light emission element irradiating light to a polygon mirror of said scanning optical apparatus on the basis of said pattern; light detection means for detecting light quantity distribution of said scan beam while receiving light by a light receiving element; movement means for moving said light receiving element in horizontal scan direction; position detection means for detecting a position of said light receiving element; and measurement evaluation means used upon detection of said scan beam based on the scan beam evaluating pattern while moving said light receiving element in beam horizontal scan direction by said movement means, for storing the position of the light receiving element detected by the position detection means, in synchronism with the scan beam evaluating pattern and evaluating position of said light receiving element according to the scan beam position detected by the light detection means and the light receiving element position detected by the position detection means.
 20. The scan beam measurement evaluation apparatus as claimed in claim 19, wherein said position detection means detects position of the said light receiving element in the horizontal scan direction as well as in the vertical scan direction, and said measurement evaluation means stores the respective positions and executes measurement evaluation of position of said scan beam.
 21. The scan beam measurement evaluation apparatus as claimed in claim 19, wherein said measurement evaluation means stores position of the light receiving element in synchronism with generation range of the scan beam evaluating pattern.
 22. The scan beam measurement evaluation apparatus as claimed in claim 19, wherein said measurement evaluation means stores position of said light receiving element in synchronism with detection trigger signal generated at the trigger position upon generation of an actual scanning pattern concerning the scan beam evaluating pattern set independently and the detection trigger position of position of said light receiving element.
 23. The scan beam measurement evaluation apparatus as claimed in claim 19, wherein said measurement evaluation means stores position of said light receiving element in synchronism with a predetermined condition, while comparing writing pixel position accumulated from reference position signal with position of the light receiving element obtained from said position detection means.
 24. The scan beam measurement evaluation apparatus as claimed in claim 23, wherein said measurement evaluation means finds as the predetermined condition a first pixel clock signal after the scan beam has passed position of the position detection means by using the beam position determined by the accumulated value of the pixel counter and the position information of the position detection means, and stores the position of the light receiving element in synchronism with this first pixel clock signal.
 25. The scan beam measurement evaluation apparatus as claimed in claim 23, wherein said measurement evaluation means finds a beam position determined by an accumulated value of the pixel counter corresponding to the position information of the position detection means, and uses a first pixel clock signal after the scan beam has passed this beam position, as the predetermined condition for storing position of the light receiving element when storing position of the light receiving element in synchronism with the first pixel clock signal.
 26. The scan beam measurement evaluation apparatus as claimed in claim 23, wherein said measurement evaluation mean generates said scan beam evaluating pattern set beforehand on the basis of the position information of said light detection means input continuously, stores, in synchronism with this, position information of said light receiving element and start position of said scan beam evaluating pattern, and executes measurement evaluation of the scan beam position on the entire scan system based respective position information.
 27. The scan beam measurement evaluation apparatus as claimed in claim 19, wherein said position detection means outputs a pulse-string signal, and said evaluation pattern generation means has counter means for counting the number of pulses in the pulse-string signal.
 28. An electrophotographic image formation apparatus having a scan beam measurement evaluation apparatus described in claim 19, for executing measurement evaluation of position of a scan beam in a scanning optical apparatus executing exposure scanning of an electrostatic latent image. 